Documents allegedly written by a deceased officer that raised questions about President Bush's service with the Texas Air National Guard bore markings showing they had been faxed to CBS News from a Kinko's copy shop in Abilene, Tex., according to another former Guard officer who was shown the records by the network.

The markings provide one piece of evidence suggesting a source for the documents, whose authenticity has been hotly disputed since CBS aired them in a "60 Minutes" broadcast Sept. 8. The network has declined to name the person who provided them, saying the source was confidential, or to explain how the documents came to light after more than three decades.

There is only one Kinko's in Abilene, and it is 21 miles from the Baird, Tex., home of retired Texas National Guard officer Bill Burkett, who has been named by several news outlets as a possible source for the documents.

Robert Strong, who was one of three people interviewed by "60 Minutes," said he was shown copies of the documents by CBS anchor Dan Rather and producer Mary Mapes on Sept. 5, three days before the broadcast. He said at least one of the documents bore the faxed header "Kinko's Abilene."

Strong's comments came as CBS News President Andrew Heyward in an interview acknowledged that there were "unresolved issues" that the network wanted "to get to the bottom of." Since the broadcast, critics have pointed to a host of unexplained problems about the memos, which bore dates from 1972 and 1973, including signs that they had been written on a computer rather than a Vietnam War-era typewriter.

"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 in an interview last night, while acknowledging "a ferocious debate about these documents."

Asked what role Burkett may have played in CBS's reporting, Heyward said: "I'm not going to get into any discussion of who the sources are."

Burkett, who has accused Bush aides of ordering the destruction of some portions of the president's National Guard record because they might have been politically embarrassing, did not return telephone calls to his home. His lawyer, David Van Os, issued a statement on Burkett's behalf saying he "no longer trusts any possible outcome of speaking to the press on any issue regarding George W. Bush and does not choose to dignify recent spurious attacks upon his character with any comment."

In news interviews earlier this year, Burkett said he overheard a telephone conversation in the spring of 1997 in which top Bush aides asked the head of the Texas National Guard to sanitize Bush's files as he was running for a second term as governor of Texas. Several days later, he said, he saw dozens of pages from Bush's military file dumped in a trash can at Camp Mabry, the Guard's headquarters.

The Bush aides Burkett named as participants in the telephone conversation were Chief of Staff Joe M. Allbaugh and spokespeople Karen Hughes and Dan Bartlett. All three Bush aides and former Texas National Guard Maj. Gen. Daniel James have strongly denied the allegations.

Suspicions that Burkett could have been a source for the CBS documents first surfaced earlier this week when Newsweek magazine reported that Mapes flew to Texas to interview him over the summer. Yesterday, the New York Times reported that a CBS staff member, speaking on the condition of anonymity, confirmed that Burkett was a source for the "60 Minutes" report but "did not know the exact role he played."

Yesterday, reporters from several news organizations were camped near Baird, Tex., outside Burkett's home, which is on a working ranch, with a gate barring access to a one-story farmhouse and a pickup truck outside. At 6 p.m. Central Time, Burkett walked to the gate on his cane with a black dog by his side to collect his mail. He refused to answer questions about whether he provided the documents to CBS.

"Get out of my way," he told the reporters. "You need to go home."

Earlier this year, Burkett gave interviews to numerous news outlets, including The Washington Post, alleging corruption and malfeasance at the top of the Texas National Guard, much of which have never been substantiated. He has also been a named source for several reports by USA Today, which reported Monday that it had independently obtained copies of the disputed memos soon after the broadcast.

Like CBS News, USA Today has declined to name the source of its memos on the grounds of confidentiality.

Burkett, who served with the Texas National Guard in an administrative capacity before his 1998 retirement, has been involved in a bitter dispute with the Guard over medical benefits after suffering from a tropical disease following a military assignment in Panama. He has told reporters that he had a nervous breakdown and was hospitalized for depression after he left the Guard.

Burkett has provided different accounts of exactly what Bush records he allegedly saw in the trash can at Camp Mabry. At times, he has described them as "payroll-type documents" and performance assessments. But in an Aug. 14 posting to a Web log, www.steveverdon.com, he said he saw "a two-page counseling statement" signed by Lt. Col. Jerry Killian, the officer named by "60 Minutes" as the author of its Bush memos.

Author James Moore, who relied on Burkett as a primary source for a book attacking Bush as having wriggled out of his Guard service, said in an interview yesterday that he did not think Burkett provided the memos to CBS. "His life is complicated enough already, and I don't know why he would make further complications for himself," Moore said.

On Capitol Hill, meanwhile, 39 Republican House members, led by Majority Whip Roy Blunt (Mo.), wrote a letter to Heyward demanding that CBS retract its report. Accusing the network of becoming "part of a campaign to deceive the public and to defame the president," the lawmakers said: "CBS reporters would not accept such behavior from public officials like ourselves, and we cannot accept it from them."

Separately, Rep. Christopher Cox (R-Calif.), citing reports in The Post and the Dallas Morning News, asked that a House communications subcommittee investigate what he called "the continued use of CBS News of apparently forged documents" intended to damage Bush's reputation and "influence the outcome of the 2004 presidential election." But the panel's chairman, Rep. Joe Barton (R-Tex.), rejected the request, saying that the oversight of network news should be left to the viewing public and news media.

In a related development, White House press secretary Scott McClellan hinted that more documents regarding Bush's National Guard service may soon be released. Asked whether officials in the White House have seen unreleased documents, McClellan called that "a very real possibility." Other officials with knowledge of the situation said more documents had indeed been uncovered and would be released in the coming days.

Staff writers Howard Kurtz and Dana Milbank in Washington and Sylvia Moreno in Baird, Tex., contributed to this report.