For Dave, the Show Must Go On : Television: Despite changes in ratings and staff, ‘doing the show every night is still the most fun of all of this,’ he says.

David Letterman sounded a little wistful as he talked about the difference between his early days in television and his role today, as a talk-show star with employees, a production company and a hugely successful program that is taking a hit in the ratings.

“Doing the show every night is still the most fun of all of this,” Letterman said in an interview before leaving for a May sweeps week of “Late Show” broadcasts from London.

“When you’re first starting out, you think (performing) the daily show is all you have to do. But then you find there’s more to it than that.”

One of the things that can happen to you is that, to much fanfare and a multimillion salary, you move from NBC to CBS, unseat the “Tonight Show” as the top-rated late-night talk show and, then, two years later, find your ratings hurt as CBS goes from first to third place in prime time.

“I’ve not been in this position before,” Letterman acknowledged. “CBS is in a bit of a slump. None of us is happy about the problem. But the only thing we can do about it is to do the very best show that we can.”

Letterman’s “Late Show” is still the highest-rated talk show in late-night TV, and its decline in ratings (10% during the last year) is half that of CBS’ prime-time shows. With its core of young viewers, it remains highly profitable, but NBC’s “Tonight Show” with Jay Leno has made significant gains in the ratings--and ABC’s “Nightline” has been beating both of them during coverage of the Oklahoma City bombing.

Letterman attributed the ratings decline to “a variety of factors,” from CBS’ loss of several key affiliated stations to problems in the prime-time ratings and the impact of “Nightline.” But the late-night host said of “Tonight,” “We seem to be reaching two different audiences. When our numbers are off, I don’t see those viewers going to NBC.”

The long-planned trip to London, Letterman said, is an example of what he means by focusing on what “Late Show” does best.

Elton John is the featured guest tonight, and other performers who are scheduled to appear include Peter O’Toole, Van Morrison, Chuck Berry and the co-stars of the cult British hit, “Absolutely Fabulous,” Jennifer Saunders and Joanna Lumley.

Letterman’s mother, Dorothy, who was such a hit as a correspondent from the Winter Olympics in Lillehammer, will be featured. Mujibur Rahman and Sirajul Islam, the New York shopkeepers and “Late Show” studio neighbors, will try cricket and other quintessentially British activities. And Letterman--who has been praised by TV critics for his comedic interactions with ordinary people--will turn his attention to Londoners in a number of videotaped segments during the week.

“The idea is to highlight the look and feel of London” the way the show tries to capture “the wonderful, odd” qualities of New York, Letterman said.

Meanwhile, at the same time that “Late Show” is facing a challenge from “Tonight” in the ratings, there have been changes in the Letterman staff. Rob Burnett, who had been the head writer, left in December to produce a sitcom starring Bonnie Hunt for Worldwide Pants, Letterman’s production company. It is expected to have a berth on CBS’ fall schedule.

In addition, Hal Gurnee, a 40-year TV veteran who has been with Letterman since his NBC daytime show 15 years ago, made public last week that he wants to do something new and is leaving the show as director and supervising producer at the end of this week. He will continue as a consultant and will be producer-director of prime-time specials for Worldwide Pants.

The new head writer is Donick Cary, who has been a writer on the show for the last three years. A new director has not been named.

Letterman said that he does not expect any major “Late Show” format changes. “We’re constantly looking for new people and new ideas,” he said, “but we’re doing exactly what we would be doing” if there weren’t a decline in the ratings or a turnover in personnel.

Letterman said that he and his producers are planning to take the show to Los Angeles for a week next season. “We have in our minds to come out sometime in the fall or perhaps after the first of the year,” he said. “We had a great time there last year.”

And what about being host of the Oscars? “I’d do it again in a minute,” he responded.

Critical and public opinion was divided on how well Letterman and his writers succeeded in their attempts to bring “Late Show” humor to the Hollywood institution this year. Some praised him as a breath of fresh air; others said that he and his writers were not respectful enough to Hollywood and movie-making. But buoyed by what ABC said was the additional attraction of Letterman, the telecast attracted 81 million viewers and was the most-watched Oscar show since 1983.

Letterman, typically, was self-critical of his performance.

“I knew that night it hadn’t gone that well,” he said. “I don’t think any of us felt like heroes afterward.”

Still, the entertainer said, “It would be great to come back to it a second year, having had the experience of doing it once before.”

But if he’s back next year, don’t look for Letterman to completely change his “Late Night” stripes to fit the hidebound telecast. Asked whether he felt he wasn’t reverential enough toward Hollywood in his Oscar humor, he laughed and said, “This is one of the biggest moneymaking shows in the world. You have to have some fun with this. Is reverence really required?”

* LENO’S ON THE MOVE

Jay Leno’s “The Tonight Show” has never beaten David Letterman’s “Late Show” for a full week, but last week CBS squeaked ahead by only one-tenth of a ratings point. F10