CBS anchor Dan Rather acknowledged for the first time yesterday that there are serious questions about the authenticity of the documents he used to question President Bush's National Guard record last week on "60 Minutes."

"If the documents are not what we were led to believe, I'd like to break that story," Rather said in an interview last night. "Any time I'm wrong, I want to be right out front and say, 'Folks, this is what went wrong and how it went wrong.' "

Rather spoke after interviewing the secretary to Bush's former squadron commander, who told him that the memos attributed to her late boss are fake -- but that they reflect the commander's belief that Bush was receiving preferential treatment to escape some of his Guard commitments.

The former secretary, Marian Carr Knox, is the latest person to raise questions about the "60 Minutes" story, which Rather and top CBS officials still defend while vowing to investigate mounting questions about whether the 30-year-old documents used in the story were part of a hoax. Their shift in tone yesterday came as GOP critics as well as some media commentators demanded that the story be retracted and suggested that Rather should step down.

"This is not about me," Rather said before anchoring last night's newscast. "I recognize that those who didn't want the information out and tried to discredit the story are trying to make it about me, and I accept that."

For Rather, 72, it is an all-too-familiar role. In his CBS career, he has survived an impertinent exchange with President Richard M. Nixon during Watergate, a clandestine trek through the mountains of Afghanistan, an on-air confrontation with George H.W. Bush over Iran-contra and a much-debated sitdown with Saddam Hussein in Baghdad.

Now, on the final leg of a career launched by a Texas hurricane, Rather is trying to weather his biggest storm. And some of his closest friends and associates are concerned.

"I think this is very, very serious," said Bob Schieffer, CBS's chief Washington correspondent. "When Dan tells me these documents are not forgeries, I believe him. But somehow we've got to find a way to show people these documents are not forgeries." Some friends of Rather, whose contract runs until the end of 2006, are discussing whether he might be forced to make an early exit from CBS.

In her interview with Rather yesterday, Knox repeated her contention that the documents used by "60 Minutes" were bogus. Knox, 86, worked for Lt. Col. Jerry B. Killian while he supervised Bush's unit in the early 1970s.

"I know that I didn't type them," Knox said of the Killian memos. "However, the information in there is correct," she said, adding that Killian and the other officers would "snicker about what [Bush] was getting away with."

Rather said he was "relieved and pleased" by Knox's comments that the disputed memos reflected Killian's view of the favorable treatment that Bush received in the military unit. But he said, "I take very seriously her belief that the documents are not authentic." If Knox is right, Rather said, the public "won't hear about it from a spokesman. They'll learn it from me."

But he also delivered a message to "our journalistic competitors," including The Washington Post and rival networks: "Instead of asking President Bush and his staff questions about what is true and not true about the president's military service, they ask me questions: 'How do you know this and that about the documents?' "

CBS News President Andrew Heyward defended the work that went into the Guard story. "I feel that we did a tremendous amount of reporting before the story went on the air or we wouldn't have put it on the air," Heyward said last night. "But we want to get to the bottom of these unresolved issues," including questions about the memos' typography, signatures and format. "There's such a ferocious debate about these documents."

Heyward said the account by Knox is "significant, which is why we're putting it on our prime-time program," "60 Minutes."

As a former Houston reporter, White House correspondent and "60 Minutes" regular, Rather has always taken pride in unchaining himself from the anchor desk to cover wars, political campaigns and various other crises. Determined not to be just a multimillion-dollar news reader like some younger-generation stars, he continued to anchor "48 Hours" before finally giving it up and to contribute pieces to "60 Minutes," even at the cost of being stretched thin. So it was not unusual for Rather to be crashing an investigative piece, as he did last week.

The most controversial of the three broadcast network anchors who took the reins in the early 1980s -- the others are ABC's Peter Jennings, 66, and NBC's Tom Brokaw, 64, who is retiring after the election -- Rather has long drawn the most headlines and the sharpest criticism from conservatives who view him as biased.

"Dan is a lightning rod, compared to Brokaw and Jennings, because of his personality," said Lawrence Grossman, a former president of PBS and NBC News. "He's had some very strange incidents. His colorful use of language makes him a little quirky in many people's eyes. So he's a little vulnerable."

But ABC News executive Tom Bettag, who once produced Rather's evening news, said his friend has been "quite extraordinary" in shouldering the burden. "He is the sort of person who could easily say 'this is a team effort,' but he's one of those anchors who puts it all on his shoulders and doesn't pass it down the line to anyone else," Bettag said.

Bernard Goldberg, a longtime CBS correspondent who has turned sharply critical of his former employer, said he believes that Rather was duped and will survive. But, he said, "CBS News is acting the way the Nixon administration did during Watergate. I'm really sad to say that Dan Rather is acting like Richard Nixon. It's the coverup, it's the stonewalling."

Nicholas Lemann, dean of Columbia University's Graduate School of Journalism, said that "if it turns out CBS got this wrong, it's very damaging." He added that Rather "has a 'hot' personality that provokes strong reactions."

That may be an understatement. Rather has a penchant for down-home Texas truisms, the sort of globe-trotting that earned him the nickname "Gunga Dan" for his Afghan foray, and plain old strange behavior -- such as signing off his broadcasts for a time with the word "courage."

In 1986, he was mugged on Park Avenue with one of his attackers shouting, "Kenneth, what is the frequency?" In 1987, the network went to black because Rather had angrily walked off the set in the belief that a U.S. Open tennis match would bump his broadcast. In 1988, he got into an emotional shouting match with then-Vice President Bush, who accused Rather of being unfair. In 2001, he apologized for speaking at a Democratic fundraiser in Texas in which his daughter was involved.

His career has seemed revitalized in the past year and a half. He landed an interview with then-Iraqi President Saddam Hussein shortly before the U.S. invaded Iraq and the first sitdown with Bill Clinton about his autobiography. And with producer Mary Mapes, who also spearheaded the National Guard story, Rather broke the news of Iraqi prisoners being abused at Abu Ghraib -- after agreeing to a two-week delay at the Bush administration's request.

Once the most watched of the three anchors' broadcasts, Rather's show has been ranked third for several years. Now he is even the target of a new Web site,

Some media analysts are already comparing the Guard controversy to the 1993 fiasco in which NBC's "Dateline" apologized for staging the fiery crash of a truck, and the 1998 debacle in which CNN apologized for the "Tailwind" story that accused U.S. troops of using nerve gas during the Vietnam War.

"Dan knows that trying to do a story about a Republican president is immediately going to stir up a hornet's nest from the conservatives who have jumped on him since the Nixon days," Bettag said. "He could have been excused for saying 'I don't need this kind of grief.' But he didn't."

As Rather signed off to rush back into the studio last night, he sounded a defiant note.

"I try to look people in the eye and tell them the truth," Rather said. "I don't back up. I don't back down. I don't cave when the pressure gets too great from these partisan political ideological forces."

CBS News's Dan Rather says "I'd like to break that story" if the documents on President Bush's National Guard service prove to be forgeries.