It's the day after Jon Stewart finished hosting an upcoming prime- time Sesame Street anniversary special, and the comic is ready to dish dirt on the muppets. "Kermit was not there," he says, then lowers his voice to a conspiratorial whisper. "I think he's in rehab."

But what's the hipper-than-thou, David-Letterman-favorite Stewart doing hanging out with Big Bird? "Just recently," Stewart cracks, "I learned to read, and they were instrumental in helping me." He turns serious, adding, "I guess they ran through a list of other people they wanted to do it and those people said no. I said yes. And it was a ball. You remember them from when you were a kid. It freaks you out. You're standing there singing a song with Bert and Ernie."

Still, don't expect a warm-and-fuzzy Stewart when he headlines a Comedy Central-sponsored show at the Barrymore Friday. His sharp brand of stand-up humor helped land him more than 10 appearances on Letterman, and he's working with Letterman's production company, Worldwide Pants, on various projects. He also performed in an hourlong HBO special last year after spending three years hosting cutting-edge talk shows on MTV and in syndication.

But Stewart, who turns 35 later this month, has been less visible this year. "One of the nice things I've been able to do is, if nothing else is going on, I'll go out on the road and do my act,'' he says.

"There are ups and downs in a career. You can be cold in a second, but you can be hot in a second. That's the bargain with the devil you make." Stewart, in fact, is speaking from a New York office, where he operates Busboy Productions, working to develop projects for Miramax Films.

At present, he just received a script for "Almost Romantic," a film he hopes to co-star in with Janeane Garofalo. The film's synopsis: "We're at a wedding and we've been friends for a long time. I kinda like her, she kinda likes me, but we have trouble admitting that to each other. The groom gets sick at the wedding, and we take their wedding package."

Stewart approaches the movie business cautiously. His experiences in recent years have been disappointing. "Basically, my filmography is two unreleased movies and one that I got cut out of.''

The latter film was The First Wives Club. "When I got the part, I told everyone, `I'm in this movie, I'm Goldie Hawn's boyfriend!' Then it's released, I'm not in it, and I'm more embarrassed than anything,'' Stewart says.

A veteran stand-up comic, Stewart got his national break working for MTV in 1993. His anything-goes talk show reached a pinnacle when Stewart wound up on guest William Shatner's lap. "I said, `You're about to go where no man has gone before.'" Although he's happy with his experience at MTV -- "They gave me a very long leash" -- he zeros in on the outlet's quality.

"It's still style over substance. That's been it's earmark since the beginning. I remember being in college [William & Mary] when it came out, thinking, `Yeah, I'm hungry like the wolf, Duran Duran is right!'" He adds, "Look, you're never going to turn to MTV like the way you turn to The Discovery Channel: `I watched MTV today and I swear to God I learned a lot.' That's not the point."

In September 1994, Stewart's show jumped to syndicated TV, but lasted only 10 months. Still, he remembers several memorable moments.

"A guy brought trained condors and one flew out in the audience, and we stood there dumbstruck while it bit an audience member's back, '' Stewart says. "I was staring at this huge bird gawking in the audience. The trainer's sitting there, `Hey, man, maybe you should go to commercial.' And I said [angrily], `Hey, maybe you should get your bird.' The next night, Marilyn Manson was on and they ended up lighting the stage on fire. I really thought somebody was going to be killed that week.'"

Jon Stewart , with opening act Dave Attell (screening of the raunchy, animated South Park follows Stewart), 8 p.m. Friday, Barrymore Theatre, 2090 Atwood Ave., $8.50 in advance and $10.50 day of show, 241-8633.