HOUSTON, July 8 - Military records that could help establish President Bush's whereabouts during his disputed service in the Texas Air National Guard more than 30 years ago have been inadvertently destroyed, according to the Pentagon.
It said the payroll records of "numerous service members," including former First Lt. Bush, had been ruined in 1996 and 1997 by the Defense Finance and Accounting Service during a project to salvage deteriorating microfilm. No back-up paper copies could be found, it added in notices dated June 25.
The destroyed records cover three months of a period in 1972 and 1973 when Mr. Bush's claims of service in Alabama are in question.
The disclosure appeared to catch some experts, both pro-Bush and con, by surprise. Even the retired lieutenant colonel who studied Mr. Bush's records for the White House, Albert C. Lloyd of Austin, said it came as news to him.
The loss was announced by the Defense Department's Office of Freedom of Information and Security Review in letters to The New York Times and other news organizations that for nearly half a year have sought Mr. Bush's complete service file under the open-records law.
There was no mention of the loss, for example, when White House officials released hundreds of pages of the President's military records last February in an effort to stem Democratic accusations that he was "AWOL" for a time during his commitment to fly at home in the Air National Guard during the Vietnam War.
Dan Bartlett, the White House communications director who has said that the released records confirmed the president's fulfillment of his National Guard commitment, did not return two calls for a response.
The disclosure that the payroll records had been destroyed came in a letter signed by C. Y. Talbott, chief of the Pentagon's Freedom of Information Office, who forwarded a CD-Rom of hundreds of records that Mr. Bush has previously released, along with images of punch-card records. Sixty pages of Mr. Bush's medical file and some other records were excluded on privacy grounds, Mr. Talbott wrote.
He said in the letter that he could not provide complete payroll records, explaining, "The Defense Finance and Accounting Service (DFAS) has advised of the inadvertent destruction of microfilm containing certain National Guard payroll records."
He went on: "In 1996 and 1997, DFAS engaged with limited success in a project to salvage deteriorating microfilm. During this process the microfilm payroll records of numerous service members were damaged, including from the first quarter of 1969 (Jan. 1 to March 31) and the third quarter of 1972 (July 1 to Sept. 30). President Bush's payroll records for these two quarters were among the records destroyed. Searches for backup paper copies of the missing records were unsuccessful."
Mr. Talbott's office would not respond to questions, saying that further information could be provided only through another Freedom of Information application.
But Bryan Hubbard, a spokesman for Defense finance agency in Denver, said the destruction occurred as the office was trying to unspool 2,000-foot rolls of fragile microfilm. Mr. Hubbard said he did not know how many records were lost or why the loss had not been announced before.
For Mr. Bush, the 1969 period when he was training to be a pilot, is not in dispute. But in May 1972, he moved to Alabama to work on a political campaign and, he has said, to perform his Guard service there for a year. But other Guard officers have said they had no recollection of ever seeing him there. The most evidence the White House has been able to find are records showing Mr. Bush was paid for six days in October and November 1972, without saying where, and the record of a dental exam at a Montgomery, Ala., air base on Jan. 6, 1973.
On June 22, The Associated Press filed suit in federal court in New York against the Pentagon and the Air Force to gain access to all the president's military records.
The lost payroll records stored in Denver might have answered some questions about whether he fulfilled his legal commitment, critics who have written about the subject said in interviews.
"Those are records we've all been interested in," said James Moore, author of a recent book, "Bush's War for Re-election," which takes a critical view of Mr. Bush's service record. "I think it's curious that the microfiche could resolve what days Mr. Bush worked and what days he was paid, and suddenly that is gone."
But Mr. Moore said the president could still authorize the release of other withheld records that would shed light on his service record.
Among the issues still disputed is why, according to released records, Mr. Bush was suspended from flying on Aug. 1, 1972. The reason cited in the records is "failure to accomplish annual medical examination."
Mr. Bartlett, the White House spokesman, said in February that Mr. Bush felt he did not need to take the physical as he was no longer flying planes in Alabama. Mr. Lloyd, the retired colonel who studied the records, gave a similar explanation in an interview.
But Mr. Lloyd said he was surprised to be told of the destruction of the pay records that might have resolved some questions.