The hardest talks over the weekend were probably taking place inside Mr. O’Brien’s camp, which is facing three options: stay, even though the show’s staff feels increasingly unwanted at NBC; look for an offer elsewhere, most likely the Fox network, which has let out broad hints that it would be interested in starting its own late-night franchise with Mr. O’Brien; or walk away and get into a probable legal battle over whether NBC breached Mr. O’Brien’s contract by making this change.

So far, Mr. O’Brien and his representatives have steered clear of commenting on their plans. But one issue that will be at the center of any negotiation over the host’s future is whether his contract is still valid because NBC will still call his program “The Tonight Show.”

Mr. Gaspin would not discuss contracts, but he said what was important to Mr. Leno was the opportunity to tell “jokes at 11:30 p.m.” and what was important to Mr. O’Brien was keeping the “Tonight” franchise.

In private comments from Mr. O’Brien’s side, however, keeping that title is more likely part of NBC’s legal maneuvering than a vital interest of the host, who is said to be upset with the moves.

Last week, Mr. Gaspin described Mr. O’Brien as “courteous, gracious and professional” in discussing the planned changes. He said the same of Mr. Leno, who, speaking with reporters in Vancouver, British Columbia, in an appearance there Saturday night, said he was basically on board with the shift  even though his show would be reduced to a half-hour.