‘Tonight’ Starring Jay Leno and . . . ? : Television: Now that he’s been named Johnny Carson’s successor, look for a new executive producer and theme song next year. But who will be the new Ed and Doc?

NBC’s anointment of Jay Leno on Thursday as Johnny Carson’s successor at the helm of “The Tonight Show” is only the first of many changes in store for the late-night program. What form most of them will take, however, Leno isn’t prepared to say.

One certainty: The show’s musical theme, written by Paul Anka, is so identified with Carson that it will have to be replaced.

“It’s like hearing ‘Thanks for the Memory’ and having everyone say, ‘So where’s Bob Hope?’ ” Leno said.

Another: Leno’s manager of 18 years, Helen Kushnick, will become the show’s executive producer, replacing Fred de Cordova.

Decisions regarding other changes have yet to be made. No new announcer has been set to replace Carson’s longtime sidekick, Ed McMahon, who will be leaving with Carson. Band leader Doc Severinsen reportedly plans to leave too and will need to be replaced. A new musical format is a possibility.

Nor has Leno considered who might occupy his current post as permanent guest host when he’s on vacation (which probably will be three weeks a year; otherwise he plans to be at the interview desk five nights a week).

“This is all so new that we haven’t even thought about it,” Leno said at his Benedict Canyon home. “Also, you’ve got to realize that this is all a year off. I don’t want any other talk shows picking up on our ideas. I think that when I’m on vacation they’ll just do reruns. That’ll amortize the product. As for the music, I like the idea of an orchestra like the one we have now. You don’t want to do the same as other shows, like David Letterman, who has a rock band. People really like ‘The Tonight Show’ orchestra.”

Although it was a virtual certainty that Leno would succeed Carson, whose career atop the late-night talk show ratings has spanned nearly three decades, NBC waited two weeks to make the news official. Carson had announced at the annual meeting of network affiliates in New York May 23 that he would leave the show as of May 22, 1992.

Leno, 41, will join the select company of Carson and his predecessors, Steve Allen and Jack Paar, who have made “The Tonight Show” an American TV institution since 1954.

“I like to look back at the history of hosts and say, ‘Gee, it’s my turn not to drop the ball,’ ” Leno said in an interview. “It’s like being given the crown jewels. You hold on to them and make sure nobody steals them. Then you pass them on to somebody else.”

Leno began guest-hosting the show in the autumn of 1987. His four-year tenure, plus his popularity with younger audiences, has resulted in both a smooth transition and a status in the ratings equal to Carson’s, which made his appointment a natural one. (Before that time, NBC had experimented with Joan Rivers and Garry Shandling as permanent guest hosts, but both went on to their own shows for other companies).

“Leno has proven extremely popular with the late-night audience and we are confident that the show will continue its late-night dominance for many, many years,” said Warren Littlefield, president of NBC Entertainment.

Leno said that he had received offers from other networks to host late-night talk shows in the past, but that he never seriously considered any of them.

“I’ve sort of been a good soldier. They (the network) sort of gave me an indication that when Johnny was ready to retire, this would go into action. It was a preparation. They’d say, ‘Can you do this?’ But I’ve worked Caesar’s in Las Vegas since 1977. I’ve had the same manager for 18 years. When I go somewhere, it’s to stay. It’s a bit like living together for five years and then deciding to get married. I like things that have a sense of history.”

For a number of years, comedy aficionados thought that Leno would make an excellent “Tonight Show” host, since he was brightly poised at the forefront of younger stand-up comedians and he worked clean. When it took so long for him to make his way to the show’s regular hosting chores, however, the conventional wisdom held that his “ethnic” look and his departure from the Midwestern WASP prototype image held him back.

But Leno’s travel schedule has been one of the most punishing in a profession characterized by frequent travel (he estimates he’s flown 3 million miles on American Airlines), and he feels that’s what led to this payoff.

“There are two ways to get a major shot on TV,” he said. “Either you stay in town and schmooze the casting directors and agents, so that you become well-known in the industry, or you build a base around the country. I’ve played every city in the country--including Alaska--at least once. I’ve worked with network affiliates, giving interviews, helping them do spots, sell tickets. I think I have them to thank. And I take it as a compliment that people can’t place me. Somebody’ll come up to me and say, ‘Aren’t you from Grand Rapids? I saw you play there.’ I don’t think I would’ve gotten this job if I’d gone through the normal testing and screening process.”

Leno’s extensive travel is one of the things that has kept him in touch with the pulse of America. Now that he’ll be restricted to the relatively insular environment of television, how will he keep his antennae out?

“After you’ve been doing this for 20 years, you learn to go with your instincts,” he said. “You know when you’ve done one Quayle joke too many. I meet ‘The Tonight Show’ audience before the show. And don’t forget, when you do a monologue every night, you can feel an audience’s reaction, pro or con. They give you a sense of what’s appropriate and inappropriate. Johnny Carson can still read an audience better than anyone.”

Although it’s a big step from living as a tenant in a house and then becoming its owner--particularly when guests, couch and repartee are witnessed throughout the country--Leno feels comfortable about the move.

“For a comedian, it’s akin to being elected president. You’re not playing a character. You get to be who you are. Laurel and Hardy never changed; no matter what period or setting they were in, they were always Laurel and Hardy. I’m exactly what people expect when they meet me. They don’t say, ‘You’re not a doctor or a detective?’ I don’t have to learn scripts or spend all day on a movie set. You tell the jokes, do the monologue, it’s all over and different the next day.”

However, “I do feel the responsibility,” he said. “I’ve always led my life as though it was understood that I had to make moral decisions. I’ll never show up drunk and embarrass ‘The Tonight Show.’ ”

Leno feels the show itself to be part of a moral tradition.

“When you think of some of the horrible things this country’s been through, the assassination of John F. Kennedy and Martin Luther King (Jr.), the Vietnam years, the fact that Johnny was able to get up night after night and find comedy in the day’s events or find some way to make people laugh, that’s a hard thing to do. Let ‘Nightline’ handle the crises and Donahue ask the probing questions. On ‘Tonight’ you want to have the lighter side. I hope it never changes.”