WILLIAM PETERSEN IS DEAD SERIOUS about his work on the hit series CSI, staying single and not stepping on bugs.

By: Rachel Abramowitz

William Petersen loves to watch animals copulate. The 48-year-old star of the new hit series CSI: Crime Scene Investigation says that perhaps his favorite video of all time is the five-part PBS series on the sex lives of animals, featuring such oddities as a species of lesbian lizards. It's somehow fitting viewing material for an entomologist -- or at least a man who plays one on T.V. Petersen stresses, however, that unlike his character, Las Vegas forensic investigator Gil Grissom, "I'm a terrible science person. It took me six years to get through high school. I hated to study."

That seems to be the primary difference between Grissom and the actor who plays him. Both are workaholics, consumed with re-creations of sorts. Indeed, Petersen, who also executive-produces the show, explains, "Here's the deal: When I'm acting, I'm a way more interesting person. When I'm on a date or in a bar, I shut down. Grissom defines himself through his problem-solving. Men often define themselves through their work, and I think there are a lot of people out there who understand that."

Apparently so. CSI is the dark-horse hit of the season, now pulling in 21 million viewers on Thursday nights after snagging a Golden Globe nomination for best drama earlier this year.

The critical and commercial adulation comes as a pleasant surprise to an actor who has long chosen the unconventional career path, preferring theater over film and Chicago over the more lucrative pastures of Las Angeles or New York. It took CBS president Les Moonves eight years to persuade the earnestly macho Petersen to try his hand at series television. Even his best-known Hollywood performances -- in the mid-"80s cult hits Manhunter Michael Mann's chilly prequel to The Silence of the Lambs, and in William Friedkin's To Live and Die in L.A. -- required his directors to seek him out. Marg Helgenberger, Petersen's CSI costar testifies to the actor's elusive nature. "Bill is a very compelling, enigmatic man," she says. "You think you know him, but the next day you realize how little you do."

Petersen was born in Chicago, the youngest of six children in a family descended from "four generations of Scandinavian furniture makers." He first discovered the world of culture when his schoolteacher mother forced him to forgo football practice once a week in order to attend a great-books class with "all the smart girls." Petersen attended Idaho State University on a football scholarship but drifted into the theatre program and wound up traveling Europe performing plays after school. And in the early 1980s, Petersen launched the Chicago's Remains Theatre. "I was always concerned about creating something I wanted to create," he says. "It's just been in the blood."

Indeed, what seems to appeal most to Petersen about CSI is the opportunity to re-crate his own little repertory company, with people "I care about, that I like." His motto for the show is "Think outside the box." He even had T-shirts made for the crew bearing a logo of a box with the work THINK outside of it.

Like Grissom, Petersen, who has a 25-year-old daughter from a failed marriage, is single. "I've had maybe five relationships, and they have all been long-standing, but I'm always gone," he says. "I had a relationship with a gal in Chicago. She's there, and I have 14-hour days here. It's just too hard. I go off to Australia to make a move, I go to the Philippines, I go to Canada.  If they want to have their lives and their careers, they can't just come along with me."

There will, however, always be enough time for bugs. "I don't kill ants anymore," says Petersen, describing the show's influence on him. He recalls a recent shoot during which they filmed a woman's corpse crawling with worms and beetles. "We put on thousands of bugs. The crew was really creeped out, but I have no problem with it. I said, 'This is how you are all going to be. You will be with the bugs and the beetles. They will restore you back to the earth. That's the job."