WASHINGTON — Bill Burkett, who has emerged as a possible CBS source for disputed memos about President Bush's Guard service, has a long history of making charges against Bush and the Texas National Guard.

But Burkett's allegations have changed over the years and have been dismissed as baseless by former Guard colleagues, state legislators and others.

Even Burkett has admitted some of his allegations are false.

Burkett wrote a long indictment against Bush for a Web site in 2003 in which he said he personally was ordered to "alter personnel records of George W. Bush." In that article, Burkett said that when he refused he was sent to Panama as punishment, where he contracted a disabling disease.

But when asked about that charge by the Houston Chronicle in February, Burkett said, "That statement was not accurate, that is overstated."

Burkett, 54, of Baird, Texas, has refused to return calls since the CBS report on Bush's Guard service ran last week.

On Thursday, the Washington Post and the New York Times named Burkett as a possible source for documents CBS used that experts have called fakes. The documents were faxed from a Kinko's in Abilene, the closest commercial copier to Burkett's home in Baird.

The CBS report used documents signed by since-deceased Texas Air National Guard Lt. Col. Jerry Killian to suggest Bush disobeyed a direct order to take a flight physical in 1972.

If Burkett is the source of the CBS documents he must have recently obtained them. In earlier interviews, he described years of fruitless searching.

One month ago, in an essay posted on a progressive Web site, Burkett theorized that Killian would have been a likely person to know more about Bush's service. But, he conceded, "I have found no documentation from LTC Killian's hand or staff that indicate that this unit was involved in any complicit way to ... cover for the failures of 1Lt. Bush .. " Burkett went on the say, "On the contrary, LTC Killian's remarks are rare."

Several people with connections to the Texas National Guard immediately suspected Burkett was the source of the CBS report last week and saw it as part of an ongoing vendetta with Bush and the Guard.

Burkett's attorney, David Van Os, said Thursday, "My client has not authorized me to talk about this matter." Van Os issued a statement saying Burkett, "no longer trusts any possible outcome of speaking to the press on any issue regarding George W. Bush."

The questions about the CBS documents' authenticity have seemingly overshadowed the larger questions about Bush's Guard service.

CBS anchor Dan Rather on Wednesday conceded there were questions about the authenticity of the documents but challenged Bush to answer questions about his Guard service. White House spokesman Scott McClellan responded by saying, "It is always best for journalists to stick to reporting the facts and not try to dispense campaign advice."

Questions remain about the documents used by CBS. Experts have said they are fake. Killian's wife and son have said they do not reflect his feelings about Bush and have called his signature a forgery. Texas Guard officials noted many technical discrepancies that they said cast doubt on the documents.

And Marian Knox, Killian's 86-year-old former secretary, said she never typed the documents and believes they are fake. But Knox said they did reflect concerns Killian had with Bush's Guard service.

If Burkett does prove to be the source of the documents, CBS got them from a man with a well-established history of Bush loathing.

In an article Burkett wrote for the Internet last year, he compared Bush to Hitler and Napoleon as one of "the three small men" who sought to rule through tyranny. "Three small men who wanted to conquer and vanquish," Burkett wrote. Burkett confirmed authorship of that article in the February Chronicle interview.

Some of Burkett's friends and associates say they don't know whether he is the CBS source.

Harvey Gough, a Dallas restaurant owner who, like Burkett, fought a legal battle against the Guard, said, Thursday, "I can't say he did it or he didn't do it." But Gough said Bush aides such as Karl Rove or Dan Bartlett could have "cooked them up" to trap CBS with a bogus story. That has been denied by Bush officials.

James Moore, co-author of the book "Bush's War for Re-Election," which quoted charges made by Burkett, said Thursday, "I know Bill has anger at Bush and the Guard, but I have a difficult time thinking he'd take that kind of risk to fabricate documents."

One person who has heard Burkett's charges against Bush and the Guard over the years is Rep. Bob Hunter, an Abilene Republican who chaired a committee overseeing the Texas Guard. Hunter agreed to let Burkett make charges of favoritism, mismanagement and abuse by the Guard at a legislative hearing in the late 1990s.

Hunter said Thursday he came away unimpressed. "He brought up matters that none of us could believe."

That Burkett's story has changed or evolved over the years is a matter of record.

During Bush's first White House run in 2000, Burkett told reporters he overheard both ends of a phone conversation between former Texas Guard commander Gen. Daniel James III and Bush's one-time Texas Chief of Staff Joe Allbaugh that he said occurred in the summer of 1997, wherein he alleged documents unfavorable to Bush were to be destroyed. That was similar to what he told Hunter's committee, the lawmaker recalled.

But that claim changed earlier this year.

In February, Burkett said he witnessed documents from Bush's records in a garbage can at a Guard base in Austin.

"My eyes fixed on the first page," he said in an interview in February. "It had Bush, George W. Lt1. What I did next still bothers me. I browsed through the top five or six pages."

Everyone who could have supported the account, including George Conn, the friend who Burkett said took him to the office, said it wasn't true. Allbaugh, now a Washington consultant, called the story, "baseless . . . hogwash."

Texas Guard officials said no Texas Air Guard records had ever been stored at the facility Burkett named.

Burkett said in interviews earlier this year that his long-standing campaign against the Texas National Guard and Bush began after the Guard failed to provide medical care for him after he contracted a tropical disease in Panama in 1998.