Ted Koppel (search), who has anchored ABC News' "Nightline" (search) since its inception a quarter-century ago, said Thursday he will leave the network when contract expires at the end of the year.

"Ted and I have discussed a number of options under which he might have remained at 'Nightline' or in some other capacity at ABC News, but Ted believes this is the right time for him to leave," ABC News President David Westin said.

Westin said he was optimistic that "Nightline" would continue with an orderly transition. Ultimately, ABC and parent Walt Disney Corp. executives will decide whether the network sticks with news in that time slot.

In its 25th anniversary year, Koppel's ABC News program has been at a crossroads, and speculations have been swirling as recently as last month about what changes the network might implement.

"Nightline"'s ratings have dropped to almost half of what they were a decade ago, though they've rebounded slightly the first few months of this year.

The future of the program and Koppel's position there were threatened three years ago when ABC tried to lure comedian and "Late Show" (search) host David Letterman (search) from CBS. And late last year, one of the program's co-executive producers stepped down, citing an inability to agree on changes.

There has been talk of swapping Koppel, who recently turned 65, with ABC's George Stephanopoulos (search), putting Stephanopoulous in the "Nightline" host slot and Koppel on the struggling Sunday morning franchise "This Week" (search).

"There has been endless speculation about 'Nightline,'" ABC News spokesman Jeffrey Schneider said in mid-February. "I expect there will be more. I'm not going to add to that speculation, except to say we are doing the finest broadcast right now and expect to continue."

But the network wanted to figure out the future of the program by year's end, since Koppel's contract was expiring by then.

Ratings for "Nightline" have been up slightly this year, reversing a longstanding trend of declining viewership.

The show averages 3.8 million viewers a night, down from 6.3 million viewers a decade ago, according to Nielsen Media Research (search).

In that same stretch, David Letterman's "Late Show" dropped from 6.3 million to 4.6 million on CBS. NBC's dominant "Tonight" show with Jay Leno (search) averaged 5.7 million viewers a decade ago and is at 5.8 million now.

"Nightline" began as a series of special reports during the Iranian hostage crisis in 1980, and was groundbreaking in its early years for how Koppel conducted live interviews with several subjects — a standard in television now but then a product of new technology.

Though it was once a relative novelty, "Nightline" has been competing in a television environment saturated by news. People have also been going to bed earlier and getting up earlier, as the increasing viewership for local early-morning news shows indicates.

Furthermore, many companies have tensions between headquarters and satellite offices, and that's frequently been the case with ABC News' New York office and the "Nightline" Washington base.

"Nightline" co-executive producer Leroy Sievers resigned in November, saying the company was considering fundamental changes to the show and "we were unable to agree on those changes."

In February, neither Stephanopolous nor Koppel was willing to talk of a possible swap or any other changes the network was considering. All others involved said then that the speculation of a new order was premature.

"We're thinking about something that is basically a year off and a lot can happen between now and then," Tom Bettag, "Nightline" executive producer, said in February.

"All of us have put a lot of years into putting together a broadcast that is unique in television and is important to viewers," he said. "We'll do everything we can to make sure it will go on another 25 years."