CBS News retracted yesterday much of a report on President Bush's military service, saying it had been deceived by a retired Texas National Guard officer who presented documents purporting to show that Bush had received preferential treatment to avoid fulfilling his Vietnam War-era obligations.

The network and its chief anchor, Dan Rather, the on-air correspondent for the original Sept. 8 report, expressed "deep regret" and took responsibility for lapses in judgment that led to reliance on the documents now disavowed by CBS.

"There's no excuse," Rather said in an interview. "I made a mistake. We made a mistake. We clearly established the documents could have been authentic. But we did not prove they were authentic."

Rather said he was unaware before his story aired that at least two of the four experts asked by CBS to authenticate the memos had expressed reservations. But he said he took responsibility for those lapses, along with his colleagues.

The network announced yesterday that it would launch an independent investigation of the breakdown of journalistic standards that allowed the documents said to be from Bush's squadron commander, Lt. Col. Jerry B. Killian, to form the basis of the recanted 60 Minutes report. CBS News President Andrew Heyward said he intended to name at least two people outside CBS to review its news-gathering process and to release a public report.

"This is something that's raised questions about our credibility," Heyward said in an interview. "The answer is that you're transparent about what you know and what you don't know. You look very candidly at your own institution. You take steps to shore up what mistakes you may have made. And you continue, day in and day out, to do good reporting."

Questions raised

Within hours of the Sept. 8 prime-time broadcast, Web loggers questioned the documents, skeptically reviewing features considered more common to modern word processors than typewriters in use in the early 1970s. By Sept. 10, mainstream news organizations interviewed professional document examiners who pointed out a series of warning signs. But the network stood by its story, calling the source of the memos "unimpeachable." On the CBS Evening News on Sept. 10 and Sept. 13, Rather summarized the growing objections but offered a pointed defense.

Last night reflected a near-total collapse of that stance.

Many conservative critics have long alleged that CBS has an ideological bias against Republicans - a contention the network vehemently rejects. But White House spokesman Scott McClellan linked the discredited CBS report to a series of Democratic assaults on Bush.

Bill Burkett, the retired National Guard officer who provided the documents to CBS, said yesterday in an e-mail circulated to reporters that his contacts with Kerry allies were limited to deflecting attacks on Democratic presidential nominee John Kerry's combat service in Vietnam.

CBS News had gained momentum this year with a series of hard-hitting stories, including broadcast of pictures revealing the Abu Ghraib prison scandal and a recent report about a possible transfer of classified information from the Pentagon to the Israeli government.

CBS' missteps on the Bush National Guard story have damaged the network's credibility in the public eye, other journalists say. In previous debacles at NBC, The New York Times and USA Today, senior figures lost their jobs.

"It's really a horror," said Lawrence K. Grossman, former president of NBC News and PBS. "I feel sorry for these guys, but it is a betrayal of people's trust in many ways.

"Someone's going to have to fall for it," he said.

Burkett, a retired lieutenant colonel, said last night on CBS that he had misled producers when he said a former Air Guard official gave him copies of the documents.

"You know, your staff pressed me to a point to reveal that source," Burkett told Rather. "I simply threw out a name that was, basically, I guess, to take a little pressure off for a moment."

But Burkett said he did not fake the documents and pointed to another source. CBS said it could not verify the identity of the second person.

Rather took pains yesterday to express his personal regret. In remarks to The Sun, Rather said he first became convinced on Thursday that the network had erred. That's when the former national guard officer acknowledged lying to CBS about how he obtained the papers. Rather flew to Dallas to tape the interview with Burkett on Saturday.