O'Brien said in a statement Tuesday that shifting "Tonight" 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. EST.
He doesn't have an offer in hand from another network, O'Brien said. 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 new 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.
Growing up watching "Tonight" host Johnny Carson and getting the chance to "one day sit in that chair has meant everything to me," and was an opportunity he worked long and hard to obtain, O'Brien said.
"Tonight" has long been the dominant late-night program on television, with O'Brien following in a line of hosts that included Steve Allen, Jack Paar, Johnny Carson and Leno. For many of those years, an appearance on "Tonight," particularly for comics, could make or break a career.
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.
Online, many took to O'Brien's defense and applauded the host's stand against NBC. "Team Conan" was one of the most popular Twitter topics Tuesday afternoon, as young viewers pledged their allegiance to O'Brien.
An O'Brien portrait also circulated as a badge of support. Referring to the "Tonight" show host's playful nickname, it read, "I'm with Coco," and featured a black-and-white picture of a regal-looking O'Brien standing in front of an American flag. The only color: his shock of orange hair.
It doesn't make sense for NBC to try and hold him to a contract, said John Rash, a media analyst for the Chicago advertising firm Campbell & Mithun.
"An unhappy comedian is not a good premise for a program," Rash said.
The late-night shuffle has played out amid speculation that O'Brien might bolt for Fox. And the network's top entertainment executive, Kevin Reilly, said on Monday, "I love Conan personally and professionally."
Fox has had trouble launching late-night shows in the past, with Chevy Chase and Joan Rivers as notable failures. O'Brien offers the advantage of being a proven performer with a team experienced in putting on a show.
"Certainly Conan has a loyal audience and he's been able to effectively position himself as a victim of NBC's schedule shuffle," said Rash, who added that the tone of O'Brien's show seems to fit Fox's brand better than it does NBC's.
ABC's top entertainment executive, Stephen McPherson, said his network had no interest in O'Brien. ABC would have sought Leno if he hit the open market, but its executives believe that O'Brien's show is so close in tone to Letterman's that it wouldn't be good competition.
Fox declined comment Tuesday on O'Brien's statement, but it is taking action that would indicate the network is seriously considering bringing O'Brien to late-night, a period now largely filled by a variety of syndicated fare that includes network reruns.
Fox is asking some of its stations to study and report back on how much money is made with current late-night programming, according to a person familiar with the request. The person spoke on condition of anonymity because the person was not authorized to publicly discuss the request.
The syndication agreements that are in place are a costly sticking point if Fox wants to put in a late-night show across the network, the person said.
It might not be easy for affiliate stations to break profitable syndication agreements, said analyst Rash.
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. But it didn't count on Leno remaining atop the late-night ratings when he was pushed out of "Tonight."
To keep Leno from becoming a late-night competitor to O'Brien at another network, NBC offered him the daily 10 p.m. EST prime-time series. The network also saw it as an opportunity for cost-cutting, with a talk show considerably cheaper to produce than the scripted dramas that typically fill the final hour of prime-time.
O'Brien said he hoped that he and NBC could resolve the issue quickly so he could do a show of which he and his crew could be proud - "for a company that values our work" - raising the possibility he might go to another network.
NBC declined comment Tuesday, adding that O'Brien was scheduled to do his show Tuesday night.
For O'Brien, it was a stark contrast to early in his career, when he was an unknown replacing David Letterman in the 12:30 a.m. slot. He suffered brutal reviews, tough ratings and was working on a week-to-week contract. But NBC's management then stuck with him, and he blossomed into a proven performer.
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 NBC broadcasts the Winter Olympics, which will dominate NBC's schedule from Feb. 12-28.O'Brien noted in his statement that he'd received sympathy calls and added that no one should feel sorry for him because he's been "absurdly lucky" to do what he loves most in a world with real problems.
He ended the statement with a punch line: "Have a great day and, for the record, I am truly sorry about my hair; it's always been that way."