LOS ANGELES - Jon Stewart need not bother. It is evident from the moment he walks into the room. It has been evident since the start of his career.

"The hardest thing for me to pull off is sincerity," he says with great sincerity, "because I've been trained to take the steam out of what's going on around me, even myself."

As we say, he need not bother to say it. Anyone familiar with Mr. Stewart's work, from his hosting duties on Comedy Central's The Daily Show, in which he pokes fun at the news and the people who make it, to his 1998 book of essays, Naked Pictures of Famous People, a funny, sarcastic collection that contains no naked pictures of famous people, knows that Mr. Stewart is a man with a serious affliction. He is afflicted with permanent tongue-in-cheek.

His glib manner and quick comic mind have served him well. They even have helped to launch a movie career, which is on display in Big Daddy. He plays Adam Sandler's roommate, who spends most of the movie on a business trip to China. It's not a huge role, but it's a start.

When someone suggests that The Daily Show has made him a star, he responds: "Oh, sure, it's a great launching pad - to yet another cable opportunity. We're talking to the Lifetime people right now."

Don't listen to him. That self-deprecating sense of humor is going to take him big places, and we're not talking about Lifetime.

Before he signed that four-year, multimillion-dollar deal with Comedy Central, replacing Craig Kilborn as host of The Daily Show, Mr. Stewart, 36, was discussed as a possible successor to Garry Shandling on HBO's acclaimed The Larry Sanders Show. The plan, obviously hatched by greedy executive types, was to milk the show with a new host, even though Mr. Shandling had departed.

That idea was rejected, Mr. Stewart says, when he suddenly remembered the TV show AfterM*A*S*H.

"Maybe people aren't that interested in Klinger back in the States," a thoughtful Mr. Stewart says of that ill-fated TV show that tried to capitalize on the popular M*A*S*H series.

There also was talk of Mr. Stewart taking over one of the coveted late-night spots on network television. After all, he had hosted a talk show on MTV. No one is sure whether he actually was asked to host a network show, but Mr. Stewart insists that he is glad he didn' t get the job.

"I don't feel like I host a late-night show now," he says of The Daily Show, which is a spoof of news programs. "I feel like I host a comedy show. One of the reasons I didn't want to do a late-night talk show is that becomes your life. Once you do it, you can see how incredibly difficult it is, how incredibly consuming it is and how tenacious you have to be with it.

"That's not what I want for myself. I'm a stand-up. That's my trade. That's what I do in between people hiring me to do other things. I want to do a variety of things, not just a talk show. I want a Lazy Susan type of career."

Simply put, Jon Stewart grew up like millions of other kids. His mother was a teacher and his father worked for RCA. The "regular, middle-class family," as Mr. Stewart describes it, lived in quiet Lawrence, N.J., and there were no early hints that young Jon would do something as irresponsible as pursue a show business career.

To hear him tell it, his childhood was full of trauma. "During puberty, my head was this size and my body was half this size. Apparently, not big with the ladies. Apparently, they're not into enormous heads and small bodies. And yet it works in cartoons.

"My face had an interesting topography," he adds. "There were certain Appalachian regions that did not make this a fun time for me. It is one of those little God-twists that just when you get interested in girls, they mess up your face."

Somehow, Mr. Stewart survived puberty and managed to graduate from college, even with a few dates under his belt. After graduation, he worked at several jobs, but nothing seemed to sustain his interest. He always loved the comedy of Woody Allen and Steve Martin, so he decided to try his hand at stand-up comedy.

He promptly failed.

"The first time I appeared on a stage was in 1987, when I was 23, " he says. "It was about 1 a.m. at the Bitter End in the Village (New York City) and I was following five Doors soundalike bands, which is probably not the best way to get a crowd in a comedy mood.

"I had about 41/2 minutes of material prepared and was only about two minutes into it when somebody in the audience called me a name. It was absolutely brutal. I didn't finish the show and I didn't get back on a stage for a long time."

But he did get back onstage eventually, and Mr. Stewart says it was because those two minutes onstage felt right for him, regardless of how badly his jokes were received.

"It was a terrible night, but I knew what I wanted to do with the rest of my life," he says. "Just getting onstage made me realize that this is what has been going on in my head the last 20 years. Knowing that, it wasn't hard to go back on a stage."

He dismisses any notion that it took courage to "get back on the horse" after he had fallen off.

"The ramifications of getting back on that stage was nothing. Learning how to take a heart out of a man's chest and restarting it; that has ramifications. If you mess that up, the man dies.

"But what ramifications are there to bombing onstage? Comedians love using death metaphors ("I really killed tonight') but the fact of the matter is that the only thing that happens is that you think you're terrible and you walk home feeling lonely."

And just when you think Mr. Stewart is the wisest and most mature comedian you ever heard, he quickly adds, "Of course, that mature attitude comes from 12 years of retrospective. At the time, it felt horrible."

Mr. Stewart, who lives in lower Manhattan with his longtime girlfriend, says he will continue to perform stand-up, write comedic material, host cable TV shows and make movies.

"You just have to keep trying to do good work, and hope that it leads to more good work. I want to look back on my career and be proud of the work, and be proud that I tried everything. Yes, I want to look back and know that I was terrible at a variety of things."