WITH AN EYE ON . . . : As Charlie’s wedding day nears, actor Matthew Fox tries to explain his jitters

Will Charlie say “I do” or “I don’t”?

After a season-and-a-half of rocky romance with the live-in nanny, the oldest Salinger family member makes the decision of his life in this week’s “Party of Five” episode.

But actor Matthew Fox, who plays the uncertain guardian of his orphaned siblings, isn’t giving away much about the show titled “The Wedding.” All he will say about the subject over lunch at a Downtown L.A. restaurant is, “Charlie has been completely overwhelmed. Between all of his responsibilities, being the oldest in the family, taking care of his four siblings, taking over the restaurant, committing to Kirsten [Paula Devic], the restaurant fire, he really has a lot on his mind. And this is a guy who began as pretty irresponsible.”

In the previous episode, Charlie realized his issue has nothing to do with monogamy, but “something’s still bothering him and the audience doesn’t know what’s going on. He now knows he would never cheat on her, but he’s still freaked,” Fox explains.

Fox, 29, never shared Charlie’s confusion. The actor’s been married for three years to Italian-born Margarita (Ronchi), whom he met at Columbia University eight years ago. The couple share a South Bay beach home.

Fox finds Charlie’s situation very credible, however. “It’s really understandable given all he’s been through. He’s got a feeling of panic. It wasn’t that way for me, but I’m a very different person.”

“Party of Five” executive producer Amy Lippman agrees. “They’re very different,” she says. “Charlie’s a free spirit, irresponsible and can be incredibly selfish. The qualities I see in Matthew from day to day are so different. He’s incredibly responsible, committed to doing good work.”

Although, she continues, “At times he’s close to the character. They share a very dry sense of humor. The funniest stuff he does is very small, not broadly comedic ... very wry moments.”

Being comedic or dramatic was never Fox’s original intention. He describes his Crowheart, Wyo., hometown as “like nothing but a post office along a highway in between two towns that are 90 miles apart.”

Attending prestigious Deerfield Academy in Massachusetts as a “PG,” a postgraduate repeating his senior year, was eye-opening and difficult for the rancher’s son.

His love and pursuit of academics and sports paid off. Fox won a football scholarship to Columbia and got a degree in economics in 1989. “I’d seen ‘Wall Street’ and I wanted to be Charlie Sheen’s character. That’s the life I wanted. It seemed fascinating.”

But financial need in senior year turned Fox to modeling and commercials (Clearasil and milk). “It was completely a side thing, just a way to make some money.”

But Fox says his agent’s advice--”You should take this a little more seriously”--led him to a crossroads, “where I was like, let’s kick this around for a little while.”

After graduation, he studied acting in New York. “The minute I started, I was completely fascinated by it and wanted to pursue it,” he says enthusiastically. “It was never like a bolt of lightning that came down and said, ‘This is my dream I’ve always wanted to do and just never knew it.’ The more I uncovered, the more passionate I got about it. Then not too long ago I became really convinced it was something I wanted to do.”

His first role was in a February, 1992, episode of NBC’s “Wings,” followed by the lead in the feature “My Boyfriend’s Back.” Other TV work included CBS’ “If I Die Before I Wake,” and the failed 1992 CBS series “Freshman Dorm.”

And while life’s not quite a party for Charlie, this week’s episode “really starts off a really new path with him,” Lippman says. “It’s the one relationship on the show that we’ve played throughout the course of the series. Other romances and relationships have come and gone. The wedding has culminated since Episode One of last year.”

Charlie’s made a decision, Lippman says. “He lives in his father’s house, takes care of his father’s children. His life has been set for two years now, and he’s thinking, ‘How do I define my life? What responsibility do I have to myself? I’ve been responsible to kids almost over 30 episodes and I’m on the brink of this marriage and putting on brakes.’ From here on in, we’re exploring a different kind of relationship to this family.”

“Party of Five” airs Wednesdays at 9 p.m. on Fox.