to be

After reporting on Conan O’Brien for more than a decade, I figured I knew all there really was to know about the next host of “The Tonight Show.” But that was before I heard about the air conditioner.

Turns out, America’s most likable late-night host has a temper to match his 6-foot-4 frame. It flares up during rehearsals and tapings of his “Late Night” show, conducted most weekday afternoons inside NBC’s Studio 6A in New York.

“I hate being part of something that’s unfunny,” O’Brien says. “I’d rather get shot in the leg – I mean where there’s bone, not just a flesh wound, with a high-caliber bullet – than do a show that was disappointing.”

And so it was, after one sketch some years back went terribly wrong, the host stormed out of 6A and into a production closet with a low drop ceiling. He punched through the ceiling with both arms, felt something, grabbed hold and pulled down…

“… this coolant system, which is about the size of that table,” O’Brien says, “pulled it down through the ceiling – there are wires sparking – went over, picked up a phone and called a page. She came in and just stared at it. I said, ‘Could you do something with that?’ “

Telling the story now, O’Brien is hilariously self-effacing. But it’s easy to forget that late-night hosts are comedians, and comedians with few exceptions are angry people.

Johnny Carson’s wrath was fearsome, by all accounts, while David Letterman’s behavior so alienated the higher-ups in Burbank that he lost “The Tonight Show” to Mr. Nice Guy, Jay Leno.

The ceiling-punching incident also says something about O’Brien’s passion for television.

Behind that laid-back, self-mocking, “can you believe I’m on TV” persona, behind that goofy shock of red hair that he refers to as a “French dessert,” is a veteran of 2,100 hours of late-night TV who has not faced serious competition in 10 years.

Indeed, he is pulling in more young viewers (ages 18 to 34) than David Letterman is on CBS, and Letterman’s show airs an hour earlier.

O’Brien’s work ethic, though invisible to viewers and guests, has established him as the host whose interviews, daring comedy and cutting-edge musical acts are worth staying up for.

And they will make him a worthy heir to late night’s biggest prize when he takes over “The Tonight Show” in 2009 in an orderly succession that NBC brokered with Leno last October.

When he went to sign the deal giving him the “Tonight” job, O’Brien realized he was sitting in the corporate office where, at his career low point in 1994, he was forced to waive his old contract – with its one-year renewal clause – and sign a new one giving NBC the right to review his employment on “Late Night” every 13 weeks. It was that or be fired on the spot.

Now, “The Tonight Show” is his.

After the signing last fall, he took a phone call. Carson was on the line. For 10 blessed minutes, O’Brien got to talk shop with the king. He listened as Johnny told him about the show that was once named for him.

Three months later Carson would be dead.

“I still can’t really believe that he talked to me,” O’Brien said at a recent forum sponsored by the Television Academy. “If I get hit by a bus tomorrow, they can’t take that away from me.”

NBC hasn’t said whether O’Brien will move west to Burbank, where “Tonight” is now taped, or “Tonight” will head east, back to where it originated 51 years ago under Steve Allen.

For his part, the host-elect swears he hasn’t thought about what he’ll do differently once he steps onto that larger stage, wherever it is. He calls it “an abstraction” and says it’s a potential distraction as well.

“It’s this miraculous thing that I think about every once in a while, like when I’m walking the dog,” O’Brien said in a phone interview. “The thing that got me there was this show, and the easiest way to screw this up is to take my eye off the ball.”

Recalling the day in May 1993 when NBC told the world that he – an obscure writer for “Saturday Night Live” and “The Simpsons” – would be replacing Letterman on “Late Night,” O’Brien said: “I know this sounds corny, but I felt a responsibility to continue what Dave had started. This show is an experimental place for comedy, and that’s become rarer and rarer on network television.

“I want to keep that going. I don’t want to phone in the last couple of years of ‘Late Night.’ We’ll think about this other thing as we get closer.”

Some of “Late Night’s” best-loved routines go back to O’Brien’s first weeks on television.

Even now, when the show wants to put its own perverse spin on the day’s news, it calls on Robert Smigel, its former head writer, for a gag known internally as “Clutch Cargo.”

Named for the ultra-low-budget kids’ show of the 1960s, it’s the one where O’Brien pretends to interview a newsmaker via satellite, when it’s really just a picture of, say, Michael Jackson with Smigel’s lips superimposed over the mouth. Smigel’s impressions are as comically bad as ever, yet the shtick never seems to grow old.

There remains a low-budget, low-expectations feel to “Late Night” and probably always will. But the host, who now makes several million dollars a year, is the first to admit that times have changed.

“When I started in ‘93 I was such an outsider, as far outside the business as anyone on television can be,” O’Brien said. “And what we’ve done is sort of grow our own Rat Pack. On our 10th anniversary show we had Will Ferrell and Gwyneth Paltrow and Jack Black and Ben Stiller.”

NBC has digitized all 2,000-plus hours of “Late Night” and put it on a corporate server.

“My assistant, Patrick, has one of those giant computer screens, and I’ll walk by and he’ll be chuckling,” said O’Brien. “Patrick’s 22. He’ll be watching my time-travel show, where I’m in a toga, interviewing Martin Scorsese. I don’t even remember when that was.”

Neither do many of his current viewers.

“Last night there were these 16-year-old girls in the audience with homemade T-shirts,” O’Brien said. “They’ve only been fans of the show for two years. They don’t even remember that Andy Richter was my sidekick. It’s inconceivable.”

Those are the viewers who will make him late night’s biggest star in the coming years. But he has to keep them tuning in, and that’s what keeps complacency at bay.

“I’ve seen so many comedians shoot past me on the ladder in the past 12 years and become a big deal. Then their 10 minutes are up,” he said.

“But I’ve always said I hope my biggest night in show business is our last one.”