HOLLYWOOD — Monday: Sheila Rivera learns a producer from Martin Short’s television talk show will scout her upcoming Laugh Factory performance.

This is the sort of break unknown comedians dream about. TV talk shows-even Martin Short’s-are the Schwab’s drugstore counters of today. They’re where you go to get discovered. Network executives and sitcom creators watch these shows, or so it is imagined, searching for new talent. An appearance can make a career.

Tuesday: Rivera spends the day honing her act. Unknown comics are told they have to be more than funny-they have to be somebody. The idea is to create an image, a brand name, something to separate them from the hundreds of other aspiring comedians in Los Angeles. Rivera searches for a magical 10 minutes that will touch the most marketable bases of her biography.

She’s got plenty to work with: Puerto Rican childhood, engineering degree, NASA scientist, two marriages, two kids. Reducing her complicated existence to an advertisement is not something she particularly enjoys, but the necessity has been drilled into her. Feed the beast. Give it what it wants-a package.

“Hollywood works the way Hollywood works,” she says. “Comics complain, ‘They want you to be this, to do that.’ Hey, you don’t like it, leave. Screw artistic integrity. If you have to tap-dance, you better buy the shoes.”

Wednesday: She tries out new material, seeing if those new shoes fit. They don’t. “I watched the tapes this morning,” she says. “Believe me, it was painful.” Rivera is prepared to do what it takes to make it, yet resists doing what she’s told to do. It’s driving her crazy.

Thursday: Showcase day, filled with questions about what to wear, what to do, what order to put things in, she spends much of the day driving around town, doing her act in the car. She spends lots of days in the car, in part because she’s hyper and needs to move, but mainly to get out of the one-bedroom apartment she shares with two other comics and a driving-school instructor.

Thursday night, 9:30: The Puerto Rican rocket scientist storms the Laugh Factory stage. She’s wired. Her eyes are wild. She bucks and stomps like a spooked thoroughbred. She attacks the crowd, screaming.

She bombs.

Not a huge detonation; no nuclear meltdown. The crowd, in fact, laughs. It’s the television people who don’t. They leave without a word.

Strange Route to L.A.

Growing up, Sheila (pronounced Shay-la) Rivera discovered she was the only person in her family who could make her mother-a formidably dour and demanding woman-laugh.

Rivera didn’t think much of this at the time and certainly didn’t think of it as suggesting career options.

Rivera’s family moved from Puerto Rico to Texas in 1978 when she was a senior in high school, a move so frightening that she refused to go. She stayed home to finish school, then rejoined them after graduation. She spent that summer in Houston in front of the television, struggling to learn English, then went off to Texas A&M.

Her father was a salesman for IBM and urged his children into more respectable lines of work. His oldest daughter, Sheila’s sister, followed his advice, becoming an electrical engineer.

“That’s hard,” Rivera says. “I thought, ‘What’s harder than that?’ Rocket science, right?’ So I majored in aerospace engineering.”

Out of college, she went to work for McDonnell Douglas on the space shuttle program. Her job, in the orbital mechanics group, was to design a method of blowing up the shuttle’s expendable fuel tanks without raining rocket debris on people below. She liked it a lot. Or thought she did.

But one morning, just weeks, actually, after she started at Douglas, she was in her mother’s Chrysler Newport driving to work. As she approached the Johnson Space Center, the thought occurred to her that this was how she was going to spend every day for the rest of her life.

“And I thought, ‘No, I won’t.’ It seemed very confining all of a sudden. That was the beginning.”

She nonetheless stuck with engineering for seven years, then-desperate for more human contact-switched to sales. Impressed by super salesman Zig Ziglar, she moved into motivational speaking. She loved the thrill of being in front of a crowd, holding it in thrall.

She had always been the class clown, one of those people everybody laughed at and told, “You ought to be a comedian.” In 1994, she told herself that she would at least give comedy a try.

That fall she went to a seminar for aspiring comedians and did five minutes on stage. She loved it. “This is it,” she thought. “I can be completely free. I can say anything I want. It was fabulous. It was extremely natural. When I got off the stage it was, ‘Ahhh, yes.’ ”

She was hooked. She was, as they say in Texas, by-God going to become a comedian. She built an act based on gender differences.

“I’m a sensitive woman trapped in a male ego,” was how it began. Those first five minutes led to 30 minutes at a club in Austin, then a club in San Antonio. She never took another straight job.

“Of course,” she says, “it doesn’t pay. No one tells you that.”

By this time, she had married, had two children, divorced and remarried. Her husband was supportive. He had a good job. Give it a try, he said.

Houston had four comedy clubs, so a comedian could work locally about eight weeks a year. Plus, there were lots of one-nighters within a couple-hour drive-clubs, bowling alleys, motels. Not that these were all great gigs. She was the act who went up after Monday Night Football, when the audience was likely to be three guys ticked off because their team lost.

“They didn’t want to hear jokes,” Rivera says. “Texas style is like, ‘That’s cute, honey, now take off your shirt or get off the stage.’ ”

She went on the road for weeks of one-nighters across Oklahoma, Nebraska and the Dakotas, playing Holiday Inns and Doubletrees, taking the 80-buck paychecks and driving all day to the next show. She played big rooms in Indian casinos, places that could seat 500, but which on a Tuesday night in February might have seven, six of them drunk, half of the drunks snoring.

Rivera prides herself on her toughness. Show business people, she says, are forced to live like roaches-that is, miserably, but for a long time. Comedians, she says, are the toughest of the tough. “There are roaches that live in trees and roaches that live in sewers. Television performers are tree roaches. Comics are down in the drink,” she says.

Rivera set out to be a comedian, not an actor, but enough catcalls and sleeping audiences can drive a person to do strange things. Last fall, five years into her comedy career, Rivera packed up and moved to Los Angeles, dreams of sitcom riches dancing in her head.

It wasn’t an easy decision. Her supportive husband decided maybe he’d done enough supporting and said he wasn’t going along, which meant she would have no money, which meant further that her kids must stay behind. Friends wondered if she were nuts, or worse, selfish, a mother abandoning her children. Rivera loves her kids-a boy, 14, and girl, 11-and the thought of losing them wasn’t something she even wanted to contemplate. The children would stay with their father in Texas only temporarily, until school let out. She gave herself nine months to make or break a career.

She packed up her car last fall and drove alone to California. Once here, she ducked down into roach survival mode. She was determined. This sewer roach wanted to move up to the trees.

Being Funny, Getting Rich

Hollywood is based on a simple equation: Dreamers in, dreams out.

While every other variety of California dream comes and goes-often with frightening speed- Hollywood’s allure continues. New tastes and technologies go boom or bust-it doesn’t matter. The dream factory grows.

First came the movies, then television and the recording industry, then cable and the Internet. Whatever the medium, the global appetite for American pop culture booms.

Entertainment is widely credited with pulling Southern California out of its post-Cold War recession. Three-quarters of a million people work in the industry or in services that directly support it. Two-thirds of all the entertainment jobs in the country are in Los Angeles County, making Hollywood the capital of a new world. The rush to sit atop it is unrelenting.

This time of year, spring, the frenzy peaks in an annual exercise known as pilot season, when the networks fill the casts of new shows being considered for spots on next autumn’s prime-time schedules.

Thousands of men, women and children annually stream into Southern California for this, looking for the break that will send them into the show-business stratosphere. For comics, this moment beckons with particular urgency.

Making people laugh is for the most part a terrible way to make a living.

Consider how many-or, more to the point, how few-places there are to do comedy. Most comedy is performed live in night spots of one sort or another. They could be comedy clubs, dance clubs, dinner clubs, Moose Lodges or plain old bars. Most of these places have static clienteles. Their customers don’t change that much and while some people might come back night after night to hear a favorite singer sing favorite songs, no one will sit through the same jokes night after night. A song remains beautiful. A joke does not remain funny. Most comics don’t have more than an hour of current material. If the material doesn’t change, the audience has to. So comics move. Typically, their longest engagements are two weeks, but most are one-night stands. It’s an itinerant life full of long drives, cheap hotels and mean drunks.

It used to be that people who wanted to be comedians put up with this because that was the way it was. They had no choice.

Then, in the 1970s and 1980s, stand-up comics like Robin Williams and Bill Cosby hit it big on television situation comedies. Cosby, in fact, became America’s richest comic actor. Light bulbs, dim though they might have been, went on all over Hollywood. Sitcoms are a long-time staple of prime-time television. What better and easier way to create them than to build around people known to be funny: comedians.

Never mind that there might or might not be any relationship between stand-up comedy and acting, suddenly, Hollywood became the place to be if you were an aspiring comic. The lure of sitcom gold has become the governing dynamic of the comedy business.

‘How Can I Be More Latino?’

Sheila Rivera got lucky. Within weeks of coming to Los Angeles, armed with introductions from friends of friends, she landed a one-time shot at the Laugh Factory, which along with the Improv and Comedy Store, forms a sort of Holy Trinity of comedy, fabled places where Williams, Jim Carrey and Steve Martin rose to prominence.

Jamie Masada, the Laugh Factory owner, liked what he saw in Rivera well enough to hire her as a regular and to become her manager. “That first time, I think she’s something special,” Masada says. “There’s an intelligence, a wit. Plus, she’s a Latino woman-crosses all the barriers.”

He didn’t, however, like her act well enough to tell her it was great. What he told her instead was that she needed to work on her packaging, to emphasize her Latin heritage.

Before coming to Los Angeles, Rivera had lived in only two places-Puerto Rico and Texas. In neither of those places did anybody ever tell her she needed to work on her packaging, which was, she thought, just fine.

She’s 38 (but says, under instruction from Masada, she can play 25). She’s mobile, lithe and quick-witted. She has light brown skin, dark eyes and hair and an elusive ethnicity.

Moods don’t simply play across her face, they transform it. When pleased, she’s open, playful, ready to laugh at everything; depressed, doors slam shut, she’s midnight on a moonless night; angered, it’s still midnight, still no moon, and the sky crackles with small-arms fire.

Rivera is an observational comic. Her hero is George Carlin, not Roseanne. She doesn’t do characters and isn’t keen on making herself into one. She doesn’t want to bare her soul onstage.

She’s more apt to do a joke about anti-lock brakes-Who wants brakes that come to a graddd-uuu-al stop?-than about Puerto Rican culture. She does Mom jokes, gym jokes, fart jokes; smart, mainstream, conventional stand-up jokes.

Too generic for Masada’s tastes. He wants her to develop a look, to emphasize her background, to be the Puerto Rican rocket scientist.

She’d rather tell you about screwing up a right turn on red, but She listens to Masada, who, after all, is as plugged into the agent-producer network as anyone in town. He has nurtured other comics to success. She’d be a fool, she says, to ignore his advice. So she’s written more Latino material, more rocket science stuff.

She does a bit now that starts: “I used to be a rocket scientist. I had to quit because I make mistakes. Apparently, that’s not allowed.

“Everybody makes mistakes, but we’re not allowed to because if you’re a rocket scientist, you’re supposed to know everything, some kind of brilliant super being that can program a VCR.”

She says she goes home and tells her mom they’ve lost the Hubble space telescope.

“It’s not your fault,” her mother tells her. “It’s those mirror people.”

“But mix the reds and whites in the wash and turn somebody’s underwear pink and you’ll never hear the end of it. You? You call yourself a rocket scientist?”

The act has genuine potential.

The night of the showcase for the Martin Short people, she had prepared all the stuff Masada recommended-lots of Latino jokes, lots of rocket science. She went up on stage to do it. You could see the disorder in her sharp-featured face. Or maybe it was confusion.

Pretty soon, she was doing fart jokes, penis jokes and teasing the audience about who was going to do what to whom after the show. The crowd loved it, but this wasn’t ideal television pitch material.

“I knew what I was doing,” she said days later, when she was finally willing to talk about it. “I sabotage myself every time. My ego takes over. You’re always being told your packaging isn’t good enough. The Latino thing is the trigger. I’m always being told to be more Latino. How can I be more Latino? I am Latino. . . . I’m always being told, ‘You’re too young, too old. Too this, too that.’ It’s all marketing.”

She complains the would-be marketeers have forgotten the essence of comedy.

“Comedy is not about a look. It’s about what you are and what you say. A comedian has to have something to say. The past year, I’ve been trying to comply with what I was being told. Finally, I said screw it. I have to be me.”

It was, she admits ruefully, an inopportune time for an outbreak of ego.

Bringing God Into the Room

People are funny. Well, some people are funny. Others aren’t. This guy, right now, for example. It’s another Thursday night at the Laugh Factory, a usual Thursday-pretty good crowd, pretty good bill of pretty good unknown comics dying to get on stage. A skinny little guy is up there now, all ears and eyes and really bad material.

With the competition for stage time, comics can go weeks without working and, given that comics live for laughs, when they haven’t heard any for a while their self-doubt builds to levels that could be considered normal only in a psychiatric ward.

“They’re strange people,” says Masada. “But you got to realize where they’re coming from: tragedies, bad childhoods, divorces-whatever’s causing it, they’re lacking love. The applause is approval. The laughter is the love. And it’s so addictive. They want it. They’d shoot it up if they could.

“We had a guy in here once who beat himself up. Literally. He’d hit himself in the face. And keep hitting himself. One hand, then the other. It gets a laugh. He keeps doing it. Now they’re really laughing and he’s really slugging himself. He’s bleeding.”

This guy on this Thursday night isn’t that bad. At least he’s not physically beating himself. But he might as well be. He’s standing there, head twisted sideways, staring down at the ground, hand on his chin, brow all knotted up.

It’s uncomfortable. Off to the side of the stage, the other comics are complaining. They’re mad because the guy wasn’t on the bill. Masada stuck him in there and he’s using up their time. The audience, though, is loving it. The guy is staring at the floor muttering inaudibly and they’re happy.

The guy is Chris Rock, the hottest young comic in the world. He stopped by to try out new material and Masada let him go up. It’s Masada’s standard practice to let name-brand comics come in to work out new stuff. It lends an air of anticipation to every show and endears Masada to the big acts. Rodney Dangerfield, who is now 78 years old, stops by most weekends and does 10 minutes. He needs the hit.

Rock’s best comedy is fueled by rage, an assault on the human condition.

Tonight, the aspect of the condition that most bothers him is marriage, specifically his own. The problem with marriage, he says, is you’re not supposed to sleep with other people, which isn’t exactly how he phrased it but you get the point. Rock is greatly aggrieved by this, as if somebody had pulled a fast one on him.

“Nobody tells you that,” he says, his voice a low, sad complaint. This isn’t on the face of it very funny, but the crowd is generous, laughing, happy to see somebody famous.

A couple nights later, Rock is back. He has tucked and trimmed and the material is starting to fit. Now, the problem of faithfulness is expressed as the glory of a first kiss, as if, he says sweetly, God were pressing two heads together.

“It’s all downhill from there,” he says.

The despair is still there, but it’s cloaked in sympathy. He’s saying we’re all just clowns, falling down. One day, this is really going to be funny. It isn’t yet, but nobody tells Rock he needs to repackage his act, to cut out all that depressing stuff.

“If you’re known,” Rivera says, “you can do anything you want and they’ll laugh at you just because you’re you.”

If you’re not, everybody gets to tell you what to do.

Rivera can be a compelling presence on stage-vibrant and sophisticated, with the liberating ability to say things you might think but won’t speak. That’s where the laughs come from for her.

She notices a young couple seated next to the stage one night. The woman is dressed to the nines, right down to her stiletto heels.

“Oooh, look at you, look at you,” Rivera says. “Somebody’s gonna get laid tonight.” The crowd roars.

“You’re in control of those people. In that moment, when you have it, it’s yours. The payoff is right now. You get a rush,” Rivera says later. “You bring God into the room. It’s the feeling that everything’s OK, right now. For that moment, you save people. For that time when they’re laughing, they’re not the person who has a mortgage, who has a life outside. Nobody’s going to take them to jail.”

One night after her set, a guy in a white shirt and loosened necktie wanted to talk to her. He looked enough like a show-business type, a potential contact, she let him and he launched into a spiel about an anti-gravity machine he’s invented.

“Guy comics get girls,” she says. “I get a guy with a UFO.”

It’s insult to injury. Rivera has substantially more at risk than some 22-year-old on a lark. She scattered the remains of her former life-family, friends, six-figure-income-like so much confetti on the wind. It’s no fun, coming from a nice little ranch house on a suburban cul-de-sac, two-car garage and a trampoline in the backyard, the American Dream, to this:

She makes maybe $400 a month. She sleeps on a fold-out chair. Her personal area amounts to 18 inches of hanging space in a hall closet and the one-square-foot top of a stereo speaker cabinet on which to array pictures of her kids. She keeps her shoes in the trunk of her car.

“Would I go back?,” she says. “No. Absolutely not. I am not ever going to do that.”

It’s February. Her kids are moving out when school ends in May. The clock is ticking.

One day, out of nowhere, she says: “I can’t stand my act any more.”

Pause.

“No, it’s OK.”

Pause.

“I hate it. I’m going to get a daytime job. Just something, anything.

“Anything away from the food industry. I don’t want to be asking, ‘Do you want fries with that?’ Maybe, I’ll sell jewelry. I used to sell jewelry.”

Pause.

“Really, it’s all right.”

Long pause.

“You just gotta tell yourself, one day they’ll know who you are.”