Jay Leno, expressing what he called "surprise and disappointment" with NBC executives, said yesterday that he believed his performance as the host of the "Tonight" show should have more than satisfied the network and that he did not deserve to be threatened with losing the leading show in late-night television to David Letterman.

"Am I crazy?" Mr. Leno said in a telephone interview. "The ratings are going up, the advertisers are happy and so are the affiliates." And yet Mr. Leno said he had not received any assurances from NBC executives in New York that he would not be dropped in favor of Mr. Letterman by Jan. 15. That is the deadline NBC is facing to match a CBS offer to give Mr. Letterman about $16 million to star in a nightly talk show at 11:30, the same time as the "Tonight" show.

"I am disappointed," Mr. Leno said. "I feel like a guy who has bought a car from somebody, painted it, fixed it up and made it look nice and then the guy comes back and says he promised to sell the car to his brother-in-law." Go Elsewhere? 'Of Course'

Mr. Leno said he would "obviously leave NBC immediately" if the network decided to give the "Tonight" show to Mr. Letterman. He said he would absolutely refuse to do a show in the 12:30 A.M. spot now occupied by Mr. Letterman's show, "Late Night," and would indeed consider creating the same problem for NBC that Mr. Letterman's proposed deal with CBS caused.

"Would I go to CBS if they asked me?" Mr. Leno said. "Of course. I'm not going to do some little happy hour from Omaha at 12:30."

In the last week, factions inside NBC have been taking sides between Mr. Leno and Mr. Letterman. "NBC's West Coast executives have said everything is O.K.," Mr. Leno said of Warren Littlefield, the president of NBC Entertainment, and John Agoglia, the president of NBC Enterprises.

"But the East Coast people won't say that," he added. Specifically, Mr. Leno said he had heard from Robert C. Wright, the president of NBC, to whom both West Coast executives report. "He said they don't know what they're doing yet," Mr. Leno said. "I appreciate the candor, but it does disappoint me."

The comedian became the host of the "Tonight" show in May after Johnny Carson retired after 30 years on the show. At the time, NBC chose Mr. Leno over Mr. Letterman for the position. 'A Guy With Two Girlfriends'

Now it faces the same choice, but the stakes are much higher. Beyond the $16 million to Mr. Letterman, NBC would have to pay Mr. Leno about $10 million if it breaks its commitment to him to be the host of "Tonight." NBC now pays Mr. Leno $3 million a year as the host of "Tonight."

"NBC is like a guy with two girlfriends who doesn't know which one he's going to marry on Jan. 15," Mr. Leno said. "And the longer you wait, the madder they both get."

He said NBC's indecision was hurting him even if he survived the Letterman threat, because the network executives were letting it be known publicly that they have some doubts about him, doubts, he said, that are unjustified. 'This Isn't About Dave'

To compound the emotional aspect of the conflict, Mr. Leno acknowledged his own debt to Mr. Letterman. "I would not have this job if not for Dave," he said. Mr. Letterman had Mr. Leno on his own show as his most frequent guest in the early 1980's. "This isn't about Dave. Dave is worth whatever somebody wants to pay him. Anything I can do toward keeping him at NBC, I'd do." Short of giving up his own show, that is.

"It's a tricky situation," Mr. Leno said. "Dave is truly a star and terrific, and this is a terrible position NBC is in. But fragging your own soldier doesn't make any sense to me."

He argued that he ought to have satisfied NBC by now because his ratings have shown growth in recent weeks, after a period of turmoil when Mr. Leno's former manager and the show's former producer, Helen G. Kushnick, enraged NBC executives with her tactics in booking guests. 'We Have Great Morale'

NBC fired her. Since then, Mr. Leno said, the show has been running smoothly. "We have great morale," he said. "Everybody is having fun, except for some long faces when we read all these bad things about the show in the newspapers."

Mr. Leno reached about a 4.9 national rating in recent weeks, which is up from a low of about 4.2 in the summer. (Each rating point represents 931,000 homes.)

"I've always said, 'Just judge me by my performance,' " he said. "I've done stand-up comedy for a lot of years. When I go out and see a full house of 3,000 people, I know I'm making money for somebody. If I see only 1,200 people and the house is half-full, I know I've got to do another show to make it up to the guy. But the affiliates, the advertisers, they're all happy."

Mr. Leno said he would not be reluctant to have to face-off against Mr. Letterman at 11:30 each night. "In the comedy clubs I used to say, put me on after Richard Pryor," Mr. Leno said. "Competition is really the only way you get better."

Despite the indecision in New York, Mr. Leno said he did not believe that NBC would force him out. "I don't think it will happen," he said. But he added, "I'm not sure, and that's the annoying part."