The ''Transformers'' star talks about growing up in Hollywood, ''Indiana Jones,'' and living out of the spotlight

Three days before his 21st birthday, Shia LaBeouf has made a life-altering decision. From here on out, he’s promised himself, no more mistakes. These days, as he sits perched at the edge of megastardom — and at a table at an outdoor café in Burbank — he can’t afford to do the stupid things guys do when they have too much money and time on their hands. This year alone, LaBeouf has starring roles in no fewer than three big Hollywood pictures (showing his range by playing a voyeur, a penguin, and a robot-battling kid). And then there’s that role Steven Spielberg just tossed his way — presumably as Indiana Jones’ son. ”My life’s got to be flawless,” LaBeouf says, firing up a Parliament. ”It’s pretty simple when you think about it: Just don’t f— up.” If only it were that easy. As LaBeouf takes a break from rehearsing fight scenes for Indiana Jones 4 on this Friday afternoon, there are already reminders of how challenging it can be to be young and famous. A swarm of paparazzi helicopters just zoomed overhead, racing to West Hollywood to photograph Paris Hilton’s return to jail.

Career perils and pitfalls are nothing new for LaBeouf, a former tween star (the Disney Channel’s Even Stevens) who has already endured several cycles in the It Boy hype machine, building a catalog of well-received performances as soulful delinquents (Holes, A Guide to Recognizing Your Saints), plucky dreamers (Project Greenlight’s Battle of Shaker Heights, The Greatest Game Ever Played), and precocious sidekicks (I, Robot, Constantine).

Still, it’s a tough career path, moving from comic-relief character actor to potential hero-for-all-demographics. In April, he made his leading-man debut in Disturbia, a Rear Window for the MySpace generation that became a surprise hit after nabbing a $22 million opening weekend. Earlier this month, he was the top-billed voice performance in Sony’s CGI penguin extravaganza Surf’s Up. Now he’s gearing up for the July 4 release of Transformers — director Michael Bay’s pyrotechnic toy-story-on-steroids — in which he plays a brainy teen charged withsaving the world from impending robocalypse. ”Transformers was insane,” says LaBeouf, who spent the shoot dodging explosions that felt a little too close for comfort. ”I’m not going to die for a movie. But it was either man up or get fired.”

Transformers was co-produced by Paramount and DreamWorks, the latter of which seems to have all but adopted LaBeouf. ”If DreamWorks had a store, Shia would be on their T-shirts like Mickey Mouse,” says Disturbia director D.J. Caruso, who was drawn to LaBeouf’s Everyguy charm. ”Steven said Shia reminded him of a young Tom Hanks. Next thing you know, the whole company’s riding on him.”

That’s a lot of pressure for this lanky dude in ratty jeans and a Dodgers cap, who still looks more like a Slurpee-machine attendant than a movie star. LaBeouf’s path hasn’t followed any of the prescribed beats involving stage moms and summers spent at theater camp. He spent much of his early childhood as an urban urchin scraping to survive in the gangland of L.A.’s Echo Park. ”My parents didn’t have jobs, my dad was selling drugs, it was a bad life,” says LaBeouf, whose mom, Shayna, sold beads on the street for extra cash while his father, Jeffrey, a Vietnam vet and onetime rodeo clown, was in and out of rehab for heroin addiction. ”There were maybe two years when it was stable. Then it was just chaos.”

Fueled by sheer desperation for a paycheck, Shia, an only child, decided to give acting a shot. He found an agent in the phone book and charmed his way into the title role on Even Stevens. With money rolling in, and his dad cleaned up, the family was on solid ground. For the first few years, acting was nothing more than an easy payday — until he stumbled into a one-man master class in drama with Jon Voight on the set of his first movie. ”If Agent Cody Banks had come along instead of Holes, my life would be very different,” says LaBeouf, who says Voight gave him nightly homework assignments to study great performances, like John Hurt’s in The Elephant Man. ”He has a God-given gift for truth and authenticity,” says Voight. ”And he’s a little beyond his years in terms of self-examination.”

Talking about survival strategies in Hollywood, LaBeouf sometimes sounds a bit like an M.B.A. giving a PowerPoint presentation. ”You don’t want to flood the market with yourself,” he’ll say, projecting little of the wise-child innocence he brings to the screen. Or: ”They put you in this little shoe box and every time a certain role comes up they pull it out. I want to fit into every kind of shoe box. Comfort and typecasting are the two killers of a career.”

Drugs, alcohol, fancy cars, mansions, and public displays of dumb fun of any kind are also forbidden. ”It could all go away tomorrow if I’m at a club drinking like an a–hole,” warns LaBeouf, who drives a nondescript Nissan and lives in a two-bedroom house in the Valley. ”Someone like Lindsay Lohan’s personality is [more] famous than her performance. You’ve got to maintain some mystery.” But doesn’t he worry that all work and no play might make Shia a dull boy? ”Part of me wants to go out and see my peers. But if I go to a club and get my picture in the press, then I am that young Hollywood a–hole. That would shatter my world.”

No matter what he does, LaBeouf’s world is about to undergo a major shake-up once Transformers thunders into theaters around the globe and Indy-mania obliterates his privacy. Fortunately, LaBeouf has been too busy to worry about much beyond keeping up with Harrison Ford’s muy macho fighting skills. His palms are covered in thick calluses, and his index finger is crosshatched with gashes. ”This is the most masculine thing I’ve ever been involved in,” he says. ”Harrison set the bar in the first three movies — we’re not doing the stuntman deal. So when you come to set and you’re the new guy, you gotta buck up.”

What exactly that entails is still anybody’s guess, since details of the script are being kept top secret. LaBeouf’s been well trained in the art of vagary and displays a ninja-like avoidance of specifics. ”All I think about are weapons and crazy choreography,” he whispers. ”If I were to show you what I’m rolling around with in my glove box, I’d get arrested. I swear to God.” He pauses and scans the shabby hot-dog joint across the street. ”You learn to live with [keeping secrets] when Steven looks at you and goes, ‘I’m counting on you, kid,”’ he says, then adds dryly: ”There’s a sniper up on that roof ready to shoot if I say something.”

It’s hard to blame him for proceeding with extreme caution, considering how much he’s got at stake. ”There’s no way you get Tom Hanks’ career without thinking about this stuff,” says LaBeouf, who has decided to forgo a massive birthday blowout when he turns legal in three days. ”Everyone turns 21,” he says, flattening his last smoke on the hot pavement before hopping in his car, cranking up the speed metal, and heading back to rehearsal. ”Not everyone gets to be in Indiana Jones.”