Military payroll records that could more fully document President Bush's whereabouts during his service in the Texas Air National Guard (search) were inadvertently destroyed, according to the Pentagon.

In a letter responding to a freedom of information request by The Associated Press, the Defense Department said that microfilm containing the pertinent National Guard payroll records was damaged and could not be salvaged. The damaged material included payroll records for the first quarter of 1969 and the third quarter of 1972.

"President Bush's payroll records for those two quarters were among the records destroyed," wrote C.Y. Talbott, of the Pentagon's Freedom of Information and Security Review (search) section. "Searches for back-up paper copies of the missing records were unsuccessful."

In February, the White House released some payroll and medical records from Bush's Vietnam-era service to counter Democrats' suggestions that he shirked his duty in the Texas Air National Guard.

Bush was in the Texas Air National Guard from 1968 to 1973, much of the time as a pilot, but never went to Vietnam or flew in combat. Sen. John Kerry of Massachusetts, the Democratic presidential candidate, is a decorated Vietnam veteran, and some Democrats have questioned whether Bush showed up for temporary Guard duty in Alabama while working on a political campaign during a one-year period from May 1972 to May 1973.

Bush had asked to be able to transfer temporarily from the Texas Guard to an Alabama base during that time so he could work on the Senate campaign of a family friend. Reports differ on how long he was actually in Alabama, but it's generally believed that he returned to his Texas unit after the November 1972 election. The White House says Bush went back to Alabama again after that.

The Pentagon letter was sent in response to an April lawsuit filed by the AP under the federal Freedom of Information Act (search). That law requires government agencies to make public information not specifically exempted for disclosure.

The letter said that in 1996 and 1997, the Pentagon "engaged with limited success in a project to salvage deteriorating microfilm." During the process, "the microfilm payroll records of numerous service members were damaged," the letter said.

This process resulted in "the inadvertent destruction of microfilm containing certain National Guard payroll records," including Bush's, the letter said.

Trying to calm the political unrest, the White House on Feb. 13 released Bush's Vietnam-era military records to counter suggestions he shirked his duty. But there was no new evidence given at that time to show that he was in Alabama during the period when Democrats questioned whether he performed his service obligation.

The records showed that Bush, a pilot, was suspended from flying status beginning Aug. 1, 1972, because of his failure to have an annual medical examination. His last flight exam was on May 15, 1971. There were no new documents, during that February release, to shed any light on Bush's service in Alabama.