ABC is trying to persuade David Letterman to switch his late-night talk show from CBS, a bold move that would oust Nightline from the time slot it has held for two decades.

Letterman's representatives are talking with ABC and CBS, where he has worked since moving from NBC in 1993, according to sources close to the negotiations who spoke on condition of anonymity.

ABC and CBS representatives declined comment on Friday.

Rob Burnett, CEO of Letterman's production company, Worldwide Pants, said: "Dave's contractual obligation to the Late Show concludes this August. We are continuing negotiations with the CBS television network. It would be inappropriate at this time to discuss any inquiries that we have received from other networks."

Letterman has been the longtime No. 2 in the ratings behind NBC's Jay Leno in the late-night comic wars. He's long been unhappy that CBS' older prime-time audience and the weak local news programs on CBS affiliates don't provide him with a stronger lead-in.

He's also said to be unhappy with the pace of negotiations with CBS, according to The New York Times, which reported on the talks Friday.

ABC has a younger audience than CBS, although its prime-time ratings can't compare to CBS and have slipped markedly over the past year.

Nightline began as a regular show in 1980, an outgrowth of the Iranian hostage crisis, and still has original host Ted Koppel. But ABC is reportedly concerned that its ratings are slipping and, like most news shows, attracts an older audience that is undesirable to advertisers.

Koppel, who is returning from a vacation, was not available for comment Friday. His producer, Tom Bettag, did not return a call for comment.

Whether ABC is successful in getting Letterman for the 11:35 p.m. time slot, it may have an unhappy Nightline staff on its hands. The network will talk to Nightline about other opportunities on its schedule, including in prime-time, sources said.

There appeared to be some dispute among the parties about whether Letterman still has the contractual right to continue talks with ABC or whether CBS has an exclusive period to talk to him.