“It has been cooperative and collegial, and his coming here today was a very clear message from him that he’s not bitter and that he wants to go out on top,” Mr. Graboff said.

NBC will try to assure that, Mr. Graboff said, by making Mr. Leno’s last show on “Tonight” an event  as long as Mr. Leno wants it that way. “We’ll do whatever we can and whatever Jay wants to give him the proper send-off,” he said.

In the meantime NBC is refusing to concede that Mr. Leno’s departure to another network  as in ABC, in Mr. Kimmel’s nightmare scenario  is a fait accompli. Mr. Graboff said NBC was continuing to work on ideas with Mr. Leno across all divisions of the company. “We believe in this day and age there’s room for him to be on our air,” he said, though he added that it would not be in a show at 11:30 p.m.

One way may be some combination of television and the Internet, though that would not seem to fit Mr. Leno, who has dominated in late-night ratings on television for more than a decade, as much as it would a newer comic.

One such comic is Jimmy Fallon, who is set to take over the “Late Night” show from Mr. O’Brien when he moves up to “Tonight.” The NBC executives did not set a specific date for Mr. Fallon’s first show, though they said it was likely to be in March or April. That would mean Mr. Fallon would get the benefit of the big ratings lead-in from Mr. Leno for a number of weeks before the transition to Mr. O’Brien.

Lorne Michaels, the longtime “Saturday Night Live” boss who is also the executive producer of Mr. Fallon’s forthcoming show, said in an interview that he wanted to have Mr. Fallon start unofficially long before that. He plans to initiate an Internet version of the show before it begins on television.