Johnny Carson, 65, has finally made it official -- he'll step down as host of NBC's "The Tonight Show" on May 22, 1992, ending 30 years as the undisputed king of late-night television.

Carson had made it clear when he recently signed a one-year contract with NBC taking him through next season that he had no plans beyond then. Thursday, in a joke-filled appearance before NBC affiliate managers meeting in New York, he announced his final broadcast date.

Speculation immediately began on when or if Jay Leno -- who also recently signed to continue as "exclusive guest host" of "The Tonight Show Starring Johnny Carson" -- would be named permanent replacement.

But NBC Vice President Curt Block cautioned yesterday that "no announcement on the successor is imminent. We will spend the immediate future reflecting on Johnny's announcement. Obviously, 'The Tonight Show' will continue."

When he appeared before the affiliates late Thursday in Carnegie Hall, Carson spoke of "hanging around backstage with all the people from NBC -- all the personalities. ... Jay Leno kept driving me nuts, coming up every few minutes: 'How you feeling? How you feeling? Feel okay?'

" 'How's your thyroid? Okay? Your thyroid okay?' I said, 'I'm fine, Jay.' Jay's a good friend. I like Jay Leno, and as a matter of fact he is very concerned for my health. In fact, he suggested that I jog through Central Park about midnight tonight."

It is expected that Carson's sidekick, Ed McMahon, will also retire next year.