THE NEW TV SEASON : Conan the Unknown Makes Debut : The new host of ‘Late Night’ is not a household name--yet. ‘I think the bet here is that if I can get comfortable and be myself on TV, people will have a good time.’

It is nearly Monday night, time for Cinderella to go to the ball.

Four months ago, Conan O’Brien, a 6-foot, 4-inch 30-year-old writer and producer on “The Simpsons,” stood at a press conference humorously fielding friendly questions (“virtual unknown?--let’s have none of that--I am a complete unknown,” he said) while encircled by photographers who shouted for his attention. And so the plot-line of an unknown being chosen as the successor to David Letterman began to unfold.

Late one night last week, reality--actually doing “Late Night With Conan O’Brien” five nights a week in the highly charged late-night sweepstakes, beginning with the premiere at 12:35 a.m. tonight on KNBC--had sunk in.

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O’Brien and his young staff of writers looked weary as they emerged from a meeting in which the day’s practice show had been critiqued by Lorne Michaels, the “Saturday Night Live” executive producer who is also executive producer on the new show. They have been working long hours, assembling a staff, creating and, in the last three weeks, producing 11 top-secret practice shows before an audience in the renovated Letterman studio at NBC.

In one of the practice shows last week, O’Brien was funny and charming while interviewing Phil Donahue, and the audience laughed and seemed to be rooting for him in his opening monologue, when he joked that his friends had told him years ago, “The day you get your own talk show is the day when there will be peace in the Middle East.”

Later, settling his long legs behind a desk in his office, O’Brien seemed confident but surprisingly serious and earnest about his new show.

“When people read that a writer was hired to do a talk show, I think they had this image of this guy who was closeted away, wearing spectacles and shyly writing,” said O’Brien, assuming a Clark Kent pose. “It was as if someone opened the door and said, ‘You, we’re going to put you on camera.’ And the writer said, ‘Pardon me? Well, if you think so. Is this where I stand?’ ”

In fact, O’Brien said: “There’s obviously a huge element of luck in my getting this, but it doesn’t seem as great a leap to me as it might to some people. As a writer, I’ve always interacted with other writers to create material. I’m not a stand-up comic, so I’m not going to pretend to be. What I have, I think, is an ability to bounce off what other people do and make them laugh. That’s what a talk-show host does.”

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After hearing O’Brien’s humorous remarks at a birthday party for NBC President Bob Wright, fellow guest Johnny Carson advised O’Brien to be himself on his new show. “I think the bet here is that if I can get comfortable and be myself on TV, people will have a good time,” O’Brien said. “Of course, the fact that it’s so personal is also what makes it scary. If I went out and did ‘Hamlet’ Monday night and they panned me, I could say, ‘What do you want? The play’s no good--there are no laughs in it.’ ”

Producer Michaels, who helped launch the careers of John Belushi, Dan Aykroyd and other comedy stars, promoted O’Brien as the successor to Letterman and believes that O’Brien has the stuff to succeed.

“It’s a gamble using an unknown,” Michaels said, “but I think Conan will do fine. He’s funny, intelligent and playful--he’s always been one of the funniest people in the room (among writers and performers),” said Michaels, for whom O’Brien worked as an “SNL” writer for three years before signing on with “The Simpsons.”

“Conan is going to make some mistakes but he gets better every night we do the show,” Michaels said. “Ultimately, I think talk shows come down to whether or not you like the host, and I think people will like Conan.”

The new show--which has a couch and a band (led by Max Weinberg from Bruce Springsteen’s E Street Band)--will not be a radical departure from the talk-show form. But, O’Brien said, it will have some elements that reflect “a somewhat silly, absurdist” style of comedy. In the practice show, there were some videotaped pieces that poked fun at talk shows, along with a surprise “guest,” an actor playing President William Howard Taft. The show, said head writer Robert Smigel, an alumnus of “Saturday Night Live,” will include the use of comedy actors from time to time.

Although O’Brien was twice president of the Harvard Lampoon, a launching pad for witty TV comedy writers, he and Smigel hired only one former writer from the Lampoon. There is one writer who comes from “The Ben Stiller Show”; others are relatively new to TV. The producers said that the style of the show will evolve over time, but it sounds as if O’Brien’s show will be more collegial--and collegiate--than mean. “It’s always very hard to describe comedy, but I think Conan has a playfulness that will appeal to people our age,” said Smigel. “He may come out from behind the desk one night and start singing.”

The guests for the first night will be John Goodman and Drew Barrymore; later in the week, the lineup ranges from Mary Tyler Moore and former White House aide Mary Matalan to actor Morgan Freeman and the musical group Radiohead. Stocking the first week with several longtime TV stars (including Ed McMahon), producer Jeff Ross said, is no accident. “Conan is a TV buff, and these are people that he’ll have fun talking to.”

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O’Brien does plan to do an opening monologue on the show. “I’ll be telling some jokes,” he said, “but I’m not going to try to do anything like the political monologue that Jay Leno does.”

O’Brien and his staff are trying to separate themselves from the late-night wars between Leno, Letterman and all the rest at 11:30 p.m. Their show, which airs at 12:35 p.m., is not expected to draw as big an audience and, they hope, will be allowed to develop in more peace. “If the other shows are the combatants in World War II, we’re the (peaceful) Dutch,” joked Michaels.

NBC executives, who signed him to a $1-million-a-year contract, are said to be hopeful about the rookie’s chances. And Michaels, who signed on as executive producer of the late-night show for two years, said that he is committed to making the show work. But the pressure is clearly on O’Brien. “If I said I didn’t feel any pressure, I would think you should call NBC security and have them escort you out of here,” O’Brien said jokingly. “I may get kicked around for awhile at first, but I think this is going to work out over time.”