Eventually the game became leapfrog -- and then chicken. In the end the stakes would grow huge. Two networks with different ambitions and agendas would escalate the game into a showdown, looking to control the biggest share of the $70 million-plus profits in late-night. And the two comics in the middle would find themselves firing off jokes into the night on separate stages instead of sharing jokes on the same one.

WHEN "LATE NIGHT WITH DAVID Letterman" went on NBC, in 1982, Letterman did not forget how much he admired Leno's command as a stand-up. Two months into the new show, Letterman brought on his old Comedy Store colleague.

"Late Night" immediately had a signature guest to pair with Dave; future Leno appearances would consistently boost the show's ratings. As good as that was for the show, it was far more important to Jay Leno; he had been on "The Tonight Show" four times and ultimately bombed. In the chemistry between Dave and Jay, Leno finally found his television voice. It was the completion of a circle. David Letterman had helped launch his own career by watching Jay Leno work in the clubs. Now Jay Leno was using his guest shots with Letterman to jump-start his career.

The Letterman-Leno act began to generate a lot of good press. Nobody paid closer attention to buzz in the media than Brandon Tartikoff, president of NBC Entertainment. Tartikoff never stopped scouting new late-night talent. Leno returned to "The Tonight Show," then made several popular guest host appearances. In 1986 Tartikoff made a deal that would set up Jay Leno as the permanent guest host of "The Tonight Show."

Throughout the late 1980's the arrangement worked out perfectly -- for NBC. Letterman remained the master of the late late-night show while Leno drew strong ratings on Carson, especially with younger viewers. Leno was always cooperative with the "Tonight" staff -- a "pussycat," they called him. He was respectful of Carson and never openly coveted his job.

Letterman sensed the threat to his dream of succeeding Carson, but he had no easy way to act on it. He had grown deeply estranged from the NBC management installed by the General Electric Company after it bought the network in 1986. He had never insisted that his contract include a clause that he be guaranteed the job after Carson retired; that could have been interpreted as pushing Carson out, and Letterman would never allow that. Instead he got a guarantee that NBC would pay him a penalty of $1 million if the "Tonight" job went to somebody else. Naively, he later concluded, he hoped that would protect his interest in the show.

In 1991 sentiment had grown in some quarters of NBC's management that the "Tonight" franchise was in jeopardy. Carson was still king, but his audience was getting older, a bad development for business because television advertisers always prefer younger viewers. Though nothing was said overtly, some executives clearly believed the sooner Jay Leno succeeded Johnny Carson the better it would be for NBC's late-night franchise. Leno would never dream of pressing the point himself, but he had an advocate who did not hesitate to campaign tirelessly on his behalf. Helen Kushnick had been Leno's manager since 1975, when she spotted him at the Comedy Store. (For a brief time she had managed David Letterman as well.) Kushnick saw Leno as the comic of the future and set out to place him where she believed he belonged -- in Johnny Carson's chair.