WASHINGTON — After almost two weeks of defending the authenticity of the documents, CBS News and Dan Rather on Monday apologized for airing paperwork they now say cannot be positively identified as records from President Bush's National Guard service.

Rather and CBS News President Andrew Heyward said the documents should not have been used on the air because retired Texas Air National Guard Lt. Col. Bill Burkett, who provided them, had lied about where he got them.

"Now, after extensive additional interviews, I no longer have the confidence in these documents that would allow us to continue vouching for them journalistically," Rather said in a statement noting CBS had been "misled on the key question of how our source for the documents came into possession of these papers."

Heyward said CBS News "cannot prove the documents are authentic" and the network will commission an independent review of the process by which the report was prepared.

Rather also issued an on-air apology Monday night.

The disputed documents purport to indicate that Bush had ignored an order to undergo a physical and failed to meet his Guard obligation in the early 1970s.

David Van Os, Burkett's lawyer, acknowledged on Monday that his client had misled CBS about where he got the documents in an effort to protect the source. But Van Os also said Burkett turned them over to CBS, without vouching for their authenticity, on the promise that the network would keep his name out of it and would independently verify their authenticity.

In an interview aired on CBS Evening News, Burkett told Rather "when I sat down with your staff for the first face-to-face session before I gave up any documents I wanted to know what you were going to do with them."

"And I insisted that they be authenticated," he added.

Said Rather, "The failure of CBS News to do just that, to properly scrutinize the documents and their source, led to our airing the documents when we should not have done so. It was a mistake CBS News deeply regrets."

In addition to not knowing if the documents were authentic, Burkett also could not positively identify the person who gave them to him earlier this year, according to Van Os.

"CBS did the slickest job of coaxing and pressuring him into showing the documents, and when Bill finally showed CBS the documents it was under two major conditions," Van Os said. They were a promise of anonymity for Burkett and assurances that they would check the documents' authenticity.

"The most important thing that CBS left out of its statement . . . is that Bill did not vouch for their authenticity to the CBS producer to whom he gave copies of the documents," Van Os said.

"In his gut he has been believing that they are valid," Van Os added. "But he is the first to say, 'I'm not a document examiner. I'm not qualified to give an expert opinion, and I really don't know.' Bill went to pains to make that point to the CBS producer."

CBS declined to respond to Van Os' comments.

Van Os' comments put additional heat on Rather and CBS, who, according to Kathleen Hall Jamieson, director of the Annenberg Public Policy Center, took too long to respond to authenticity questions that cropped up shortly after the documents were aired Sept. 8 on "60 Minutes II."

"Every minute spent asking whether Dan Rather will stay or go is a minute we should spend on something else," she said, noting that the document debate has dominated political news coverage in recent days.

And, Jamieson added, it leaves Rather's future rather uncertain.

"The public will vote with its clickers," she said. "If they see a drop in ratings, he would probably announce his retirement sooner than he probably would have. The problem for Dan Rather is he defended the story after it had been challenged."

In his Monday statement, Rather said, "I find we have been misled on the key question of how our source for the documents came into possession of these papers.

"That, combined with some of the questions that have been raised in public and in the press, leads me to a point where — if I knew then what I know now — I would not have gone ahead with the story as it was aired, and I certainly would not have used the documents in questions," he said.

Rather called it "an error that was made . . . in good faith and in the spirit of trying to carry on a CBS News tradition of investigative reporting without fear or favoritism."

White House spokesman Scott McClellan said the CBS announcement leaves "a number of serious questions that remain unanswered and they need to be answered." He called Burkett "a source who has been discredited in the past" and noted media reports saying Burkett had been in touch with Democratic and Kerry campaign officials.

Van Os confirmed that his client had contacted Democratic and Kerry campaign officials but only to offer a time line based on publicly released documents relating to Bush's guard duty. Van Os said Burkett has not discussed the disputed documents with Democratic officials. He also said Kerry campaign officials never returned Burkett's calls.

However, Joe Lockhart of the Kerry campaign said he did phone Burkett — at the suggestion of CBS producer Mary Mapes.

Lockhart said Mapes asked him the weekend before the story broke to call Burkett. "She basically said there's a guy who is being helpful on the story who wants to talk to you," Lockhart said, adding that it was common knowledge that CBS was working on a story raising questions about Bush's Guard service. Mapes told him there were some records "that might move the story forward. She didn't tell me what they said."

Lockhart said he thanked Burkett for his advice after a three- to four-minute call, and that he does not recall talking to Burkett about Bush's Guard records. "It's baseless to say the Kerry campaign had anything to do with this," he said.

However, the White House called the exchange, evidence of coordination between the Kerry campaign and Burkett.

"The fact that CBS News and a high-level adviser to the Kerry campaign coordinated a personal attack on President Bush is a stunning and deeply troubling development," said White House communications director Dan Bartlett.

Democratic National Committee Chairman Terry McAuliffe, insisting serious questions remain about Bush's Guard service, said Monday nobody at his party had anything to do with the disputed documents.

The documents were part of a of CBS report that also included an interview in which former Texas Lt. Gov. Ben Barnes, a top Kerry supporter, said he helped Bush get into the Air National Guard in 1968 after being requested to do so by a now-deceased Bush family friend.

The president and his father have denied any knowledge of any strings being pulled to get Bush into the Guard at a time when many young men sought the slots as a way of avoiding service in Vietnam.

The documents — which quickly drew questions — indicated Bush ignored a direct order to undergo a physical exam to maintain his flight status when he transferred to an Alabama unit in 1972. Bush moved to Alabama to work on a family friend's political campaign.

The "memorandum for record" concerning the physical exam was signed by Lt. Col. Jerry Killian, now deceased. Two "memos to file," purportedly authored by Killian but carrying no signature, said Bush was "talking to someone upstairs" and that there had been pressure from higher-ups to "sugar coat" Bush's evaluation. One of those memos also said there had been "no feedback" from the Alabama unit as to whether Bush met his commitment there.

Marian Carr Knox, who was Killian's secretary, said the documents were not authentic, but reflected Killian's feelings about Bush.

Questions about the authenticity of the documents cropped up on the Internet shortly after CBS aired the original story. The questions centered on characteristics that indicated they had been produced on a computer, not on the typewriters generally in use by the National Guard in 1972. Atlanta lawyer Harry W. MacDougald, writing under the name "Buckhead" and posting on the conservative website FreeRepublic.com, raised the first doubt.

"I am saying these documents are forgeries, run through a copier for 15 generations to make them look old," he said in posting within four hours of the first CBS report.

In short order, several document experts joined the chorus of doubters. Even the document experts CBS used raised doubts.

Burkett, who lives in Baird, Texas, has been a longtime, high-volume Bush critic. He has told many reporters that he overheard top Bush aides order the destruction of Texas Air National Guard records as the then-governor prepared to run for president.

In a March 2003 posting on a Veterans for Peace Web site, Burkett detailed what he said was retribution from Bush for trying to get the story out.

"In January of 1998 and what seems like a full lifetime ago, I was stricken by a deadly case of meningoencephalitis," Burkett wrote, alleging he contracted the disease while in Panama on a punitive Guard mission "after angering George W. Bush by refusing to falsify readiness information and reports . . . and refusing to alter official personnel records of George W. Bush."

"George W. Bush and his lieutenants were mad. They ordered that I not be accessed to emergency medical care services; and I was withheld from medical care for 154 days before I was withdrawn from Texas responsibility by the Department of the Army, by order of the White House," Burkett wrote.

"I was a pawn then caught in a struggle for right and wrong, but also caught within a political struggle between a man who would do anything to be 'king' of America and an institution of laws that we knew as America," he wrote.

Burkett said he had to "relearn to walk and to live."

"My daily pain is far worse than anything I could have previously imagined. I suffer from extreme constant headaches, body pain and even my hair hurts," he added.

Burkett filed an unsuccessful lawsuit alleging the military had illegally denied him medical care.

Contributing: Associated Press