In fact, without the benefit of looking at his suspiciously familiar mug on the cover of this magazine, you probably wouldn't be able to place the name.

"That's the way I like it," he says. "I've never been in this business for the recognition or the awards. I just want to do good work, grab a decent paycheck, and move onto the next job." Unfortunately, all that is coming to an end for the actor whose stardom has been as elusive as his performances are effective. Think about it. His fingerprints are all over such critically acclaimed '80s flicks as To Live and Die in LA; the Silence of the Lambs prequel, Manhunter; and Cousins. In the '90s he stole the starring roles in significant TV movies and miniseries from far-more-famous actors, in such high-profile projects as The Kennedys of Massachusetts, Return To Lonesome Dove, and The Beast, where he played second fiddle to a giant rubber squid.

Still, Petersen might as well have been in the witness-protection program, for all the name recognition he received. As far as he was concerned, he had a good thing going - until now. "Because of this show, I'm screwed," he says, laughing about the new visibility foisted on him by his smash hit program. "Now I'm seen by more people in one episode than I was in 20 years of theatre and movies. It's gratifying to have an impact on 25 million people a night, but I can say goodbye to my lunch-pail life as a working actor. I'm scared I might be a celebrity."

A mountain of evidence points to it. "CSI" has ranked near the top of the Nielsen ratings for the past two seasons and has established itself as the second-most-watched show on TV, behind "Friends." Initially, the show was considered an afterthought - a convoluted concept from a first-time writer (Alan Zuiker, who was previously pulling in eight bucks an hour driving a baggage tram at Las Vegas' Mirage Hotel). According to CBS president Leslie Moonves, "CSI was not a slam dunk." Shows more about science than violence and more classroom than bedroom tend not to be big box-office on broadcast networks. But it was different enough to reel-in Petersen hook, line, and sinker.

"There has never been a show that has followed the criminalist," says Petersen, who signed on not only as star - but as one of the executive producers. "They follow the cops, and the cops are always chasing after lies. They chase down whoever is lying to them and try to get them to not lie. And these guys (the criminalists) use irrefutable evidence to pinpoint the truth. That's what drew me to it. I've been telling anybody who would listen that I wanted to do a series for the last 10 years. But I wouldn't do it if I was just another cop pushing bad guys up against the wall."

Instead he's a cop who chases murderers by gleefully plowing through piles of rotting excrement, decomposing body parts, and nasty pools of human fluids. "They're scientists and nerds," Petersen says of the show's Forensic Investigation Unit. "But with DNA and other scientific investigation techniques, they're like Sherlock Holmes for the new millennium."

He sticks a slightly less heroic label on his own character, CSI unit chief Gil Grissom. "He's more Rain Man than Spider-Man. I see him as being like one of those 12-step guys," he says. "His work has essentially replaced his life. It is his new addiction. He's more comfortable in the company of bugs and bodies than other people. He's savant-like. He needs to be the best at what he does."

What Grissom does (meticulously piece together microscopic pieces of virtually invisible evidence) has somehow become sexy to a national audience. Petersen's personal charisma plays a part in this startling development, but he thinks there's a more scientific answer to this puzzling case. "I trace this public interest back to people's hunger for answers about the O.J. Simpson verdict. People wanted to know what went wrong. The Henry Lee stuff. They [the authorities] had a mountain of evidence that amounted to a pile of crap. How did they screw that up? This show provides answers. It offers definite resolution."

"CSI" has definitely revolutionized the TV crime drama - and that suits Petersen fine. The "X-Files" suggests, "The truth is out there." CSI exhaustively demonstrates what it is. Petersen continues, "Somebody said that our show signals the end of post-modernism. America has been a nebulous society for 30 years. 'We'll try this diet this week. Let's be Buddhist for a while. We'll be vegetarians. Try yoga!' There's nothing to hang onto. People are tired of that crap. And what this show does is give you closure. It says, 'This is what happened.'"

That kind of truth is an important commodity for Petersen. He finds little of it in the world of Hollywood and celebrity. "This place is nuts," he says. "Getting back to O.J., virtually everybody believes he killed two people, and he plays 36 holes a day for the rest of his life. Bobby Blake won't get the same break. The L.A. forensic guys spent a year collecting hard scientific evidence so that won't happen again. They're gonna nail him. Celebrity won't save the killer this time. Of course, he lost his celebrity a long time ago."

No matter how much he runs from it, forensic science has helped celebrity find Petersen. The show keeps him in Los Angeles, but he remains close to his Chicago roots, spending as much time there as possible and dreading the possibility of long-term success. "Oh God, I don't know how long I can stick with this," he says. "I'd be in Chicago right now if it wasn't for this show. L.A.'s not my style. Just the other day, I had some friends in from Chicago and we went to see the Cubs beat the Dodgers out here. I was telling them there's no community here. You can't walk across the street from the stadium to the bar. I think that's a microcosm for the whole city. "

Petersen fits in as well in Hollywood as a string quartet does in a bowling alley. The blue-collar, Midwestern dude wistfully recalls his furniture-maker father taking him to watch the Bears' 1963 championship playoff game - in a bar - when he was nine. "Hey! The game was blacked-out in Chicago. We had to watch it somewhere. It's one of my favorite childhood memories." The youngest of six kids, he was a manic sports freak and a jock with unusual talents. He talks about making the football team at Idaho State as a punt returner-because he could run backwards really fast.