New York ? With the future of “Nightline” threatened, host Ted Koppel fought back Tuesday by saying it was malicious for an unidentified ABC executive to refer to the show as irrelevant.

Another veteran ABC News star, Barbara Walters, came to Koppel’s defense.

Until penning an op-ed piece that ran in Tuesday’s edition of The New York Times, Koppel hadn’t commented publicly on reports that ABC and its corporate parent, the Walt Disney Co., were courting David Letterman to replace “Nightline.”

Letterman is trying to decide whether to jump to ABC or remain at CBS, where his show is a close third in the late-night ratings after “Nightline” (Jay Leno’s “Tonight” show is first), but is considered more desirable than “Nightline” because it has a younger audience.

Koppel said it was understandable that in difficult economic times, Disney would consider replacing “Nightline” with Letterman’s more profitable “Late Show.”

But he complained about an anonymous executive who was quoted in the Times as referring to “Nightline” as irrelevant.

In the midst of the war on terrorism, when “the regular and thoughtful analysis of national and foreign policy is more essential than ever it is, at best, inappropriate and, at worst, malicious to describe what my colleagues and I are doing as lacking relevance,” Koppel wrote.

He said “Nightline” “ought to have a place in television’s expanding universe, and I am confident that it will. I continue to hope that it will be at ABC, but that decision is beyond our control.”

Walters, speaking on “The View” Tuesday, said that apparently Koppel “was one of the last to know and I don’t think that was right.” Koppel reportedly learned about the Letterman discussions Thursday night, hours before news broke in The New York Times.

Walters drew a parallel to her own tiff with ABC entertainment executives who last spring decided to move her “20/20” newsmagazine from Friday night, where it had aired for 25 years.

To not be told about such decisions ahead of time, to not be asked for an opinion, “to be treated as dispensable and irrelevant is thoughtless and hurtful,” she said.

Meanwhile, ABC News announced Tuesday that Cokie Roberts would leave “This Week” after the fall elections. She and Sam Donaldson share anchor duties on the Sunday morning public affairs talk show.

There were no plans to announce a replacement for Roberts, an ABC News spokesman said.