LOS ANGELES (AP) – 'Tonight Show' host Conan O'Brien used his best material for his statement that said he wouldn't play ball with NBC's plan for him to make room for Jay Leno to come back to late night.

By the time O'Brien arrived on stage on Tuesday night for his 'Tonight Show' monologue, his remarks about the scheduling debacle took the form of a few swipes at NBC.

"When I was a little boy, I remember watching 'The Tonight Show With Johnny Carson' and thinking, 'Someday, I'm going to host that show for seven months'," cracked O'Brien, who took over 'Tonight' from Leno last June.

"Welcome to NBC," he added – "where our new slogan is, 'No longer just screwing up prime time'."

Leno, of course, has been starring weeknights at 10 p.m. EST in a little-watched show that NBC announced earlier this week will be cancelled.

"As I'm sure you know," Leno told viewers on Tuesday in his own monologue, "NBC announced they are pulling the plug on this show February 12. Here's the amazing part: That is the exact date that the Mayan calendar predicted we would go off the air."

While Leno's return to 11.35 p.m. EST seemed definite, O'Brien's future with the network was anything but clear-cut, after he released his statement earlier in the day that abruptly derailed NBC's rush to put its late-night house in order.

O'Brien said shifting 'Tonight' to 12.05 a.m. will "seriously damage what I consider to be the greatest franchise in the history of broadcasting," and he expressed disappointment that NBC had given him less than a year to establish himself as host at 11.35 p.m.

O'Brien said he doesn't have an offer in hand from another network. Fox, which lacks a network late-night show, has expressed its appreciation for him but said this week that no negotiations have been held.

In his statement, wryly addressed to "People of Earth", the comic knocked his network's prime-time ratings woes, which stem in part from the poor performance of Leno's prime-time show. 'The Jay Leno Show' debuted in the fall after Leno surrendered his 17-year stake in the 'Tonight' last spring to O'Brien.

"It was my mistaken belief that, like my predecessor, I would have the benefit of some time and, just as important, some degree of ratings support from the prime-time schedule. Building a lasting audience at 11.30 is impossible without both," O'Brien said.

"But sadly, we were never given that chance. After only seven months, with my 'Tonight Show' in its infancy, NBC has decided to react to their terrible difficulties in prime-time by making a change in their long-established late night schedule."

'Tonight' with O'Brien is averaging 2.5 million nightly viewers, compared with 4.2 for Letterman's 'Late Show', according to Nielsen figures. And the younger audience that O'Brien was expected to woo has been largely unimpressed; O'Brien and Letterman tie among advertiser-favored viewers ages 18 to 49.

Leno was drawing around five million viewers to 'Tonight', about the same number now watching his new show.

NBC wants to move Leno out of prime-time and to the 11.35 p.m. slot with a half-hour show, bumping 'Tonight' to 12.05 a.m. – the latest it's ever regularly aired.

The network was under pressure to make a change from its affiliate stations, who found Leno's show an inadequate ratings lead-in for their lucrative local newscasts.

The network had been counting on O'Brien's cooperation, and wanted an answer quickly, so it could get the revamped schedule ready to begin airing after the Winter Olympics, which will dominate NBC's schedule from February 12-28.

NBC announced the 'Tonight Show' succession plan in 2004, well before Leno's departure, to try to avoid the Leno-David Letterman battle that ensued when Carson retired in 1992.

Leno, of course, won that battle and the job as "Tonight" host. Letterman left NBC's 'Late Night' to host 'Late Show' on CBS. Tuesday night he joked that he had received a call from NBC with the message, "Look, look, we still don't want you back".