NEW YORK (AP) – Ted Koppel, who has provided a late-night alternative to laughs as anchor of ABC News’ “Nightline” since it began 25 years ago, said Thursday he will leave the network when his contract expires in December.

Koppel, 65, said he’s not retiring. His departure casts doubt on the future of “Nightline,” although Koppel and ABC News President David Westin expressed confidence that it will continue.

The broadcast’s longtime executive producer, Tom Bettag, will leave ABC News with Koppel.

Westin had made it clear that he wanted to expand “Nightline” to an hour and air live each weeknight (sometimes it’s taped). Koppel was offered the chance to continue, or perhaps switch jobs with Sunday morning’s “This Week” host George Stephanopoulos, but told Westin upon returning from a vacation this week that he wanted to leave.

“I would have preferred Ted to have stayed a few more years, but I respect his decision and I admire his courage to walk away,” Westin said.

Koppel and ABC News executives had worked out a transition plan when he signed his last contract five years ago, but it blew up in 2002 when ABC’s entertainment division made a secret bid to lure David Letterman from CBS. Letterman chose to stay, and the incident made “Nightline” employees question ABC’s commitment to their show.

Koppel said Westin has assured him that he was not being pushed out the door.

“But who knows?” Koppel said. “Maybe it was. I’m too much a reporter and a realist, and have been in this business too long, not to recognize that my salary is very high, particularly for someone who only does three days a week now.”

He said he understands that it is harder to keep an audience and make money in a fragmented television market where there are many more options than when he started “Nightline.” As a direct competitor to Letterman and NBC’s Jay Leno, the show’s viewership has dropped from an average of 6.3 million a decade ago to 3.8 million this season, according to Nielsen Media Research.

“Maybe they feel that it’s time to give somebody younger and willing to go downmarket a chance, but I’d only be speculating,” he said. “I hope they don’t go downmarket.”

ABC has tested some new “Nightline” ideas at the network’s Times Square studio in New York, and current “Nightline” staffers have submitted a proposal to keep it in Washington. Stephanopoulos and Chris Bury lately have served as subs on nights Koppel is absent.

“It will be a somewhat different program, but it will be a program that the “Nightline’ audience will recognize and, I believe, embrace,” Westin said.

Westin is working from the assumption that “Nightline” will continue, although it’s ultimately ABC President Anne Sweeney’s decision. It’s also hard to imagine Robert Iger, incoming chief executive of ABC parent Walt Disney Corp. and a former ABC executive, won’t weigh in.

Many in ABC’s news division are hopeful, believing ABC’s entertainment division and corporate cousin ESPN have no better alternatives for the 11:35 p.m. time slot.

“Nightline” began as a series of special reports during the Iranian hostage crisis in November 1979 (originally anchored by Frank Reynolds). Then ABC News President Roone Alredge seized on the opportunity to wrest the time from affiliates, and it became a regular newscast the following March.

Koppel’s use of technology to conduct live interviews with subjects all around the world and show remote shots from far-flung places like Mount Everest – now television staples – were groundbreaking when “Nightline” started.

He also said he’s proud of the show’s efforts to investigate subjects that often didn’t get much attention on television, such as the criminal justice system. “Nightline” did some 40 shows on the AIDS crisis over the years, he said.

Koppel had been ABC News’ chief diplomatic correspondent for the decade before “Nightline” began. He joined ABC News as a general assignment reporter in New York at age 23 in 1963.

Koppel “is just a terrific reporter and as good an interviewer not only as there is today but as there has ever been in network news,” Westin said. He’s “a symbol for the best that we aspire to be.”

Bettag, who has been Koppel’s off-screen sidekick for 14 years, said the two men anticipate sticking together in some future projects.

“We’re genuinely jumping off a cliff and declaring to the world eight months before our contract is up that we’re out there looking to do good work,” Bettag said.

They may not have to look long. Koppel said a news release announcing his departure was e-mailed to the world at 10:59 a.m. on Thursday and he got his first job offer at 11:01 (he won’t say from whom).

“It was sort of lovely,” he said. “I was disappointed that it didn’t come in at 11, of course.”