When Simon Rex strolls through the lobby of a Beverly Hills hotel, beguilled women check out the chiseled face, flashing green eyes and buffed body that made him a highly paid runway model in Paris and Milan. Sinking into a chair at the bar and ordering a iced tea, the actor smiles. And why shouldn’t he? Last season, he seduced the virginal Felicity; this season, he plays bartending player Mikey on the new WB series Jack & Jill (Sundays, 9 P.M./E.T.) Rex, 25 would seem to have his career in full throttle.

Soon, however, the smiled disappears, and Rex describes his introduction to Hollywood and a mistake he made when he was 18. His is a cautionary tale of how a teenage indiscretion can haunt a star into adulthood.

In 1993, Rex appeared nude in three erotic videos that were made from a single filming. One featured, for example, Rex performing a series of gyrations on a rug and in front of a mirror. The other videos have been edited in a way that raises questions about his sexual preferences, basically, he says, giving viewers the wrong idea. “In one video, they would show me (by myself) and cut to a couple of guys together, and then cut back to me.” Now, for the first time, Rex wants to set the record straight. “I never was a porn star,” he declares. “I did one shoot. And another thing: I’m no bisexual. I’m not gay. Not that there’s anything wrong with it. It’s just not me.”

It was, in fact, the love of a woman that took him down the sex-rated route. At 17, Rex dropped out of community college in his hometown of San Francisco and moved to Los Angeles to live with a 22-year-old aspiring model and he 3-year-old son. To make ends meet, he worked as a busboy.

“I was busting my hump to make a dollar, literally,” says Rex. “We just didn’t have any money. And the time came when I found out that she was doing adult magazines, nude photographs."

Initially, he thought that was cool. And soon his girlfriend pressured him to make a porn video. “She said, ‘Simon, you’re not cutting it as a busboy,” says Rex. “ ‘I need to hook you up with this guy, and you need to do a flick.’” Rex jokes today about the multiple results. “It was kind of like a three-picture deal, like at Miramax. He (the photographer) told me it would only be seen in Germany, so I was like, ‘OK.’ I was not thinking about the future.

“It was like a Playboy video, with a girl sitting on a car touching herself,” he says. “Only this was the guy version.” He hesitates. “I had to touch myself.” Afterward, Rex says he felt “cheesy, but I never felt sexual.” He was paid $650- the exact amount of his monthly rent.

Six months later, Rex broke with his girlfriend, moved to Europe and put his porn experience behind him. “I just forgot about it,” he says. “I’ve never seen the video, believe it or not.”

Three years later, Rex had become a runway model, earning as much as $3,500 a day (his reward for keeping his clothes on) for such top designers as Versace and Armani. In 1995, he was hired by MTV as a VJ to host such shows as MTV’s Most Wanted. “I got to interview everybody, Jackie Chan and L.L. Cool J,” he says. “Really cool people. It kind of put my face out there.”

Which is exactly when the pornographic photos began to surface on gay Web sites.

Rex learned of his cyberscape debut from his mother, Zoe, who had been told by a friend. He denied it. (Zoe could not be reached for comment.)

Rod Aissa, director of talent development at MTV, remembers the day Rex told him the news. “We never thought about firingi him,” says Aissa. “Come on, we had Jenny McCarthy. MTV was more concerned with Simon’s work. And it was amazing.

Still, Rex was publicly humilated. Friends turned against him, rumors surfaced in gossip columns and strangers made catcalled. “Wherever we went- a premier, a party- people would make comments to him,” says Aissa.

Suddenly, he experienced the dark side of fame. “It kind of hit me. “Wow, this is my life. This sucks,” Rex says.

The toughest moment came when he had to tell his mother the truth. “She was crying, and she said, ‘Where did I go wrong raising you?’” he remembers. “Growing up, I was such a handful for my mom. I had to go to juvenile hall for some stupid credit card forgery and fraud. I was finally doing something with my life so that she could be proud, and (the video) surfaced.”

And it keeps surfacing whenever Rex gets a job. It followed him to the set of Felicity. Says executive producer J.J. Abrams: “I had heard that he was involved with a blue movie, but I didn’t pay attention. Then, on the day we were shooting the scene where he was making love to our heroine, I did an Internet search and found the photos. And I was just screaming, ‘No! No!’”

Abrams was concerned about a possible public-relations disaster as well as the effect on the show’s core audience- legions of teenage girls. “I could just see that they would look at this new stud and go online and freak out,” he says. Instead, he received hundreds of emails praising Rex. Abrams realized a lot of celebrities, such as onetime porn queen Traci Lords, had done worse and survived. “If I could help Simon add a more legitimate chapter to his life,” he says, “then fine.” Randi Singer, executive producer of Jack & Jill, also stands by Rex. “We don’t do background checks on our actors.” She said. “Simon was just the best one for the job.”

Rex is grateful for their support. And yet he says he is never free from the free from the fear of being penalized, which is why he finally decided to speak out. “It still lingers,” he says. “It’s good just to get it off my chest, the whole thing.”