One result of the new configuration would be that NBC would still prevent any of its late-night stars from moving to another network to start a competing show. Both Mr. Leno and Mr. O’Brien have in the past been approached by ABC or Fox about late-night shows at those networks. One reason NBC took the risky step of moving Mr. Leno to prime time was to avoid having one of its late-night stars become a competitor, a situation that NBC came to regret when David Letterman left NBC in the 1990s to start a show at CBS.

But there are many possible complications, including the possibility that Mr. O’Brien could be offered an earlier slot at a different network, most likely the Fox network. Mr. O’Brien’s representatives reported that they continued to negotiate with NBC late Thursday evening.

For Mr. Leno, who made no secret that he was unhappy about being moved from “The Tonight Show,” the change represents something of a vindication, even if his crown has been tarnished by his 10 p.m. experience. Mr. O’Brien faces a more unpalatable choice: accept a demotion to 12 a.m. and stay on NBC, or leave for another network, thereby breaking his lucrative contract with NBC.

The exact terms of Mr. O’Brien’s contract are not known, but he is rumored to have built into the deal he made five years ago to stay at NBC a guarantee that he would host “The Tonight Show” or NBC would owe a penalty of as much as $45 million. If his show continues to be called “The Tonight Show,” NBC may not be in breach of his contract, which could compel Mr. O’Brien to stay at NBC even if another network makes him an offer.

According to one senior NBC executive, his show will continue to be called “The Tonight Show,” even though it would  for the first time in its more than half-century history  not begin after the late local news. Under the plan being discussed, Mr. Leno would still host a show called “The Jay Leno Show.” The third NBC late-night star, Jimmy Fallon, has shown some promising ratings with younger viewers. He would then begin his show at 1:05 a.m., the executives said.

The revised lineup would go into effect after NBC concludes its coverage of the Winter Olympics on Feb. 28. NBC will pre-empt its prime-time and late-night lineup for more than two weeks to cover the Olympics, creating a natural break in which to make the late-night changes.

No NBC executive would speak on the record about the late-night plan. But in response to reports on several Web sites, including FTVLive and TMZ, NBC issued several statements Thursday, including one that read in part: “Jay Leno is one of the most compelling entertainers in the world today. As we have said all along, Jay’s show has performed exactly as we anticipated on the network. It has, however, presented some issues for our affiliates.”

Mr. Leno seemed to relish NBC’s predicament at Thursday’s taping. “As you may have heard, there is a rumor floating around that we were canceled,” he told his audience. “I heard it coming in this morning on the radio. So far no one has said anything to me. But if we did get canceled, it will give us time to do some traveling. I understand that Fox is beautiful this time of year.”