Jay Leno, who marked his 15th year as host of "The Tonight Show" recently, understands his role with NBC's late-night institution like a good comedian knows timing. "The real trick is you never really do own these shows. You try not to screw it up for the next person," Leno said.

"It's like the America's Cup (sailing trophy). You want to win it and you want to keep it No. 1, and when it's over you say, 'Whew, OK, your problem now.

"' The only one who could rightfully stake a claim, he said, was Johnny Carson, who presided over the NBC program for 30 years (1962-92) as its third high-profile host and the most enduring. "Obviously, Johnny owned the show and set the tone. Steve Allen was great and Jack Paar was great, but every talk show is a variation of what Johnny did.

You're always in that shadow," Leno told the Associated Press. The late-night ratings leader didn't make a big deal of the anniversary. But he planned a few surprises for Friday's show and allowed NBC to invite some

The network also set up a Web site where viewers could dabble in creating their own "Tonight" music video and promos. In an interview last week, Leno was low-key about the event. He spoke just after he'd taped a show and bolted the NBC studio, as he usually does, for his vast warehouse garage a few miles away.

His collection of rare and fast cars and motorcycles is stored there. That's one of his primary passions. Others include his wife, Mavis, a human rights activist, and "Tonight.

" "That's the real key to this (the show). It's not that you can't have a life. It just needs to become your life," said Leno, 57.

The persona he's known for is eager to toil, not so eager to blow his own horn. That attitude is the legacy of his Scottish mother, Catherine, who advised that "whatever you do, don't call attention to yourself." (His late dad's contrary credo: "Whatever you do, make sure people know you're Angelo's son.

") "I always assume I'm not as bright as the next guy, so if I work a little harder I can sort of win," Leno said. "That's why it says 'The Tonight Show with Jay Leno,' not 'starring Jay Leno,"' he said -- that was Carson's billing. Given how hard Leno fought to get "Tonight" and how much he puts into it, he's oddly sanguine about his announced, not-too-distant departure.

He plans to surrender the show in 2009 and make way for NBC's "Late Night" host Conan O'Brien, who has Leno's endorsement. O'Brien has "blossomed into a terrific talk show host, an extremely talented writer, a funny performer. He does the jokes well, does the sketches well," Leno said.

Setting an end date, he said, slams the door on a repeat of what he and his chief rival for "Tonight," David Letterman, endured as NBC dithered over filling Carson's chair. Leno had been the sole guest host since 1987 but that didn't forestall a messy selection process and aftermath in which Letterman jumped from NBC to CBS. (There is no official guest host for Leno, who famously shies away from breaks.

He let Katie Couric take over the show, once, when he filled in at "Today.