CBS News has backed off its refusal to answer questions about memos used in its “60 Minutes II” broadcast last week that said President Bush used political pressure to get out of the Air National Guard in 1973.

But the network continued its defense of the controversial broadcast.

“We established to our satisfaction, which is a high standard, that the memos are accurate or we wouldn’t have put them on television, we wouldn’t have done the report,” said CBS News’s president, Andrew Heyward, in a statement broadcast on the network.

“There was a great deal of corroborating evidence from people in the position to know about the accuracy of the memos,” he said, without specifying what the evidence was.

“Having said that, given all the questions about them, we believe we should redouble our efforts to answer those questions, so that’s what we are doing,” he added.

The report has been under a torrent of criticism from forensic document analysts, former Air National Guard officers, conservatives, and rival news outlets who derided the memos as fakes.

CBS’s statement came as ranking Congressman, Chris Cox, a Republican of California, called for hearings into the matter yesterday. Also, 40 other Republicans signed a letter sent to Mr. Heyward asking him to retract the story.

CBS anchor Dan Rather, who was also the reporter on the segment, had previously refused all requests to look into the matter, insisting that the documents were authentic and had been corroborated by independent experts.

USA Today, which also used the documents in question in a story last Thursday, announced Monday it was launching a full inquiry into the accuracy of the documents.

The debate over the authenticity of CBS’s memos has cost the network’s affiliates money and prestige, station general managers told The New York Sun.

The general manager of WCIA-TV in Champaign, Ill., Russ Hamilton, said his station has gotten between 100-125 E-mails “strongly criticizing” the [“60 Minutes II] broadcast. He said advertisers, who have traditionally understood that the networks’ news division is something he has no control over, are starting to get upset.

“We have lost a little revenue so far, nothing serious, but if this drags on, I’m not sure what’s going to happen,” he said. Mr. Hamilton declined to place a dollar figure on his lost advertising, but said the viewer’s anger and revenue drop was acceptable “given our dominant position within our market.”

KCTV’s general manager, Kirk Black, said his station, based in Shawnee Mission, Kan., said he has received about 50 e-mails from viewers, all of which “were clearly angry at CBS, and even us, for the broadcast.” He said he had seen “a slight dropoff” in advertising revenue due to the controversy, but nothing we are worried about.” He declined to give a dollar figure on lost advertising, but said his concern was prolonging the controversy, where “we – CBS affiliates have to spend more time and energy – defending the judgment of the news division. My job is hard enough.”

Last night, CBS News interviewed Marian Carr Knox, the secretary of the purported author of the documents – Lieutenant Colonel Jerry Killian, now deceased. She denied typing the documents, but said the information in them was correct, based on conversations she said she had with Killian.

CBS News had announced that it would make a formal statement yesterday morning on the integrity of the memos and CBS’s reporting process. The statement was delayed several times further until Mr. Heyward’s statement was released.

Mr. Heyward’s statement was not the first by a network insider that indicated CBS was willing to reexamine its aggressive defense of the memos. Tuesday night, CBS Washington bureau chief Bob Schieffer, who also hosts the Sunday morning talk-show “Face The Nation,” told an audience: “I think we have to find some way to show our viewers they are not forgeries.” Mr. Schieffer said he was uncertain if this could be done without compromising the identity of their sources.

A call to a CBS spokeswoman was not returned.