WASHINGTON, July 9: Microfilm records related to President George W. Bush's service in the Air National Guard three decades ago were accidentally destroyed when the military tried to improve its files, the Pentagon said on Friday.

Payroll records of large numbers of service members, including Bush, were ruined in 1996 and 1997 in a project to save large, brittle rolls of microfilm, Defence Finance and Accounting Service spokesman Bryan Hubbard said.

Bush's whereabouts during his service as a pilot in the Texas Air National Guard in the United States during the Vietnam War have become an election-year issue, with some Democrats accusing him of shirking his duty.

The destroyed files kept in Denver on deteriorating 2,000-foot rolls of microfilm covered three months of a period in 1972 and 1973 when Bush's claims of service with the guard in Alabama are in question.

"It (the film) just crumbled. We were attempting to improve the preservation," Hubbard said. He said he did not know why the destruction had not been previously announced.

The White House said it has already been shown that Bush performed his duties in the National Guard. "We released all of the documents that are available. We made that clear at the time and they demonstrate that the president fulfilled his duties in the National Guard at the time. And there is nothing new in this report," said White House spokeswoman Claire Buchan.

Last February, the White House released hundreds of pages of Bush's military records. Those records did not provide new evidence to place Bush in Alabama during the latter part of 1972, when some Democrats say he was basically absent without leave. There was no indication at that time that the pay records had been destroyed.

"This whole thing was inadvertent. It happened a long time ago at a files storage site in Denver," a senior defence official, who asked not to be identified, said.

The Defence Department's Office of Freedom of Information and Security Review said in a letter that records of a large number of National Guard members were damaged, including from the first quarter of 1969 and the third quarter of 1972.

"Searches for backup copies of the missing records were unsuccessful," said the letter, dated June 25 and signed by C.Y. Talbott, chief of the Pentagon's Freedom of Information Office.

The 1969 period is not in dispute for Bush, who was training at that time to be a pilot. 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 New York Times, which first reported the disclosure, noted that the White House had produced records showing that Bush was paid for six days in October and November 1972, but those records did not say where he was at the time. Also provided was the record of a dental exam at a Montgomery, Alabama, air base on Jan. 6, 1973. -Reuters