The network said it would appoint an independent panel to look at its reporting about the memos. The story has mushroomed into a major media scandal, threatening the reputations of CBS News and chief anchor Dan Rather.

It also has become an issue in the presidential campaign. The White House said the affair raises questions about the connections between CBS's source, retired Texas National Guard officer Bill Burkett, and Democrat John Kerry's campaign. A Kerry adviser also said he had called Burkett at the request of a CBS producer.

Rather joined CBS News President Andrew Heyward in issuing an apology Monday.

"We made a mistake in judgment, and for that I am sorry," Rather said. "It was an error that was made, however, in good faith and in the spirit of trying to carry on a CBS News tradition of investigative reporting without fear or favoritism."

Almost immediately after the story aired Sept. 8, document experts questioned memos purportedly written by Bush's late squadron leader, Lt. Col. Jerry B. Killian, saying they appeared to have been created on a computer and not on the kind of typewriter in use during the 1970s.

CBS strongly defended its story. It wasn't until a week later - after Killian's former secretary said she believed the memos were fake - that the news division admitted they were questionable.

Burkett admitted this weekend to CBS that he lied about obtaining the documents from another former National Guard member, the network said. CBS hasn't been able to conclusively tell how he got them, or even definitely tell whether they're fakes or not. But the network has given up trying to defend them.

"Based on what we now know, CBS News cannot prove that the documents are authentic, which is the only acceptable journalistic standard to justify using them in the report," Heyward said. "We should not have used them."

CBS said it approached Burkett initially about the documents. Rather said Burkett was well known in National Guard circles for several years for trying to discredit Bush's military record.

Burkett, in an interview with Rather aired on the "CBS Evening News," said he was pressured by CBS to reveal his source for the documents, and "I simply threw out a name that was basically, I guess, to get a little pressure off for the moment."

He said he didn't fake or forge any documents.

"I didn't totally mislead you," he said. "I did mislead you about one individual."

Burkett said he also insisted that CBS authenticate the documents on its own. Two document experts consulted by CBS later said they raised red flags that network officials apparently disregarded. Rather acknowledged CBS failed to properly determine whether the documents were genuine.

Burkett did not immediately return a phone call from The Associated Press seeking comment.

Besides tainting the network's flagship broadcast, "60 Minutes," the report was a damaging blow to Rather, 72. Some have suggested the scandal, along with the low ratings of the "CBS Evening News," could hasten Rather's retirement.

"Please know that nothing is more important to us than people's trust in our ability and our commitment to report fairly and truthfully," Rather said.

Alex Jones, director of Harvard University's Shorenstein Center on the Press, Politics and Public Policy, said it appeared to be an honest mistake by CBS, not a willful attempt to deceive. But he said the network was too slow to respond.

"I think that their delaying and obvious resistance to acknowledge the evident realities has kept the story alive a lot longer than it needed to be and was a lot more damaging to CBS than it needed to be," he said.

For "60 Minutes," it's the biggest ethical mess since the 1995 incident captured in the movie "The Insider," which depicted the newsmagazine caving to pressure from CBS lawyers and not airing a whistleblowing report from an ex-tobacco executive.

Jones said questions will probably center on the story's producer, Mary Mapes. She's one of the network's top investigators and broke the story of the Abu Ghraib prison abuse scandal photos.

White House press secretary Scott McClellan said the White House appreciated CBS's expression of regret but that there were still serious questions about Burkett, a Democrat.

"Bill Burkett is a source who has been discredited and so this raises a lot of questions," McClellan said. "There were media reports about Mr. Burkett having senior level contacts with the Kerry campaign."

The Kerry campaign has said it had nothing to do with the story.

A Kerry adviser, Joe Lockhart, said he had called Burkett at the suggestion of Mapes shortly before the documents were released. Lockhart said he listened to some campaign advice from Burkett for a few minutes and does not recall talking about Bush's guard records. Burkett told USA Today in a story for Tuesday's editions that his interest in contacting the campaign had nothing to do with the documents.

Asked about Mapes' involvement in the call, CBS spokeswoman Kelli Edwards said, "This is an example of the kind of thing that the independent panel that will be named in a few days will look into. When that review is complete, we will comment."

She said Mapes is not commenting on the story.

Heyward told The AP he has "no reason to believe either the Kerry campaign or the Bush campaign was involved in this."

The call for an independent review was reminiscent of CNN's "Tailwind" scandal in 1998. The cable network retracted a story that the U.S. military had used nerve gas in Laos during the Vietnam war.

CNN appointed independent panels to look into the "Tailwind" story and the missed election calls of 2000. Both panels helped to restore trust in the network and resulted in real changes to the networks' operation, said Tom Johnson, CNN's chief executive at the time.

"As with all professions, we screw up at times," Johnson said. "We need to admit it when we do."

The so-called Killian documents indicated he was being pressured to "sugarcoat" the performance ratings of a young Bush, then the son of a former Texas congressman, and that Bush failed to follow orders to take a physical. Killian died in 1984.