Documents that should have been written to explain gaps in President Bush's (search) Texas Air National Guard service are missing from the military records released about his service in 1972 and 1973, according to regulations and outside experts.

For example, Air National Guard (search) regulations at the time required commanders to write an investigative report for the Air Force when Bush missed his annual medical exam in 1972. The regulations also required commanders to confirm in writing that Bush received counseling after missing five months of drills.

No such records have been made public and the government told The Associated Press in response to a Freedom of Information Act (search) lawsuit that it has released all records it can find.

Outside experts suggest that National Guard commanders back then may not have produced the documentation required by their own regulations.

"One of the downfalls back then in the National Guard was that not everyone wanted to be chief of staff of the Air Force. They just wanted to fly or maintain airplanes. So the record keeping could have been better," said retired Maj. Gen. Paul A. Weaver Jr., a former head of the Air National Guard. He said the documents may not have been kept in the first place.

Challenging the government's declaration that no more documents exist, the AP identified five categories of records that should have been generated after Bush skipped his pilot's physical and missed five months of training.

"Each of these actions by any member of the National Guard should have generated the creation of many documents that have yet to be produced," AP lawyer David Schulz wrote the Justice Department Aug. 26.

White House spokeswoman Claire Buchan said there were no other documents to explain discrepancies in Bush's files.

Military service during the Vietnam War (search) has become an issue in the presidential election as both candidates debate the current wars in Iraq and Afghanistan.

Democrat John Kerry commanded a Navy Swift boat in Vietnam and won five medals, including a Silver Star. But his heroism has been challenged in ads by some veterans who support Bush.

The president served stateside in the Air National Guard during Vietnam. Democrats have accused him of shirking his Guard service and getting favored treatment as the son of a prominent Washington figure.

The AP talked to experts unaffiliated with either campaign who have reviewed Bush's files for missing documents. They said it was not unusual for guard commanders to ignore deficiencies by junior officers such as Bush. But they said missing a physical exam, which caused him to be grounded, was not common.

"It's sort of like a code of honor that you didn't go DNF (duty not including flying)," said retired Air Force Col. Leonard Walls, who flew 181 combat missions over Vietnam. "There was a lot of pride in keeping combat-ready status."

Bush has said he fulfilled all his obligations. He was in the Texas Air National Guard from 1968 to 1973 and was trained to fly F-102 fighters.

"I'm proud of my service," Bush told a rally last weekend in Lima, Ohio.

Records of Bush's service have significant gaps, starting in 1972. Bush has said he left Texas that year to work on the unsuccessful Senate campaign in Alabama of family friend Winton Blount.

The five kinds of missing files are:

— A report from the Texas Air National Guard to Bush's local draft board certifying that Bush remained in good standing. The government has released copies of those DD Form 44 documents for Bush for 1971 and earlier years but not for 1972 or 1973. Records from Bush's draft board in Houston do not show his draft status changed after he joined the guard in 1968. The AP obtained the draft board records Aug. 27 under the Freedom of Information Act.

— Records of a required investigation into why Bush lost flight status. When Bush skipped his 1972 physical, regulations required his Texas commanders to "direct an investigation as to why the individual failed to accomplish the medical examination," according to the Air Force manual at the time. An investigative report was supposed to be forwarded "with the command recommendation" to Air Force officials "for final determination."

Bush's spokesmen have said he skipped the exam because he knew he would be doing desk duty in Alabama. But Bush was required to take the physical by the end of July 1972, more than a month before he won final approval to train in Alabama.

— A written acknowledgment from Bush that he had received the orders grounding him. His Texas commanders were ordered to have Bush sign such a document; but none has been released.

— Reports of formal counseling sessions Bush was required to have after missing more than three training sessions. Bush missed at least five months' worth of National Guard training in 1972. No documents have surfaced indicating Bush was counseled or had written authorization to skip that training or make it up later. Commanders did have broad discretion to allow guardsmen to make up for missed training sessions, said Weaver and Lawrence Korb (search), Pentagon personnel chief during the Reagan administration from 1981 to 1985.

"If you missed it, you could make it up," said Korb, who now works for the Center for American Progress, which supports Kerry.

— A signed statement from Bush acknowledging he could be called to active duty if he did not promptly transfer to another guard unit after leaving Texas. The statement was required as part of a Vietnam-era crackdown on no-show guardsmen. Bush was approved in September 1972 to train with the Alabama unit, more than four months after he left Texas.

Bush was approved approval to train in September, October and November 1972 with the Alabama Air National Guard's 187th Tactical Reconnaissance Group. The only record tying Bush to that unit is a dental exam at the group's Montgomery base in January 1973. No records have been released giving Bush permission to train with the 187th after November 1972.

Walls, the Air Force combat veteran, was assigned to the 187th in 1972 and 1973 to train its pilots to fly the F-4 Phantom. Walls and more than a dozen other members of the 187th say they never saw Bush. One member of the unit, retired Lt. Col. John Calhoun, has said he remembers Bush showing up for training with the 187th.

Pay records show Bush was credited for training in January, April and May 1973; other files indicate that service was outside Texas.

A May 1973 yearly evaluation from Bush's Texas unit gives the future president no ratings and stated Bush had not been seen at the Texas base since April 1972. In a directive from June 29, 1973, an Air Force personnel official pressed Bush's unit for information about his Alabama service.

"This officer should have been reassigned in May 1972," wrote Master Sgt. Daniel P. Harkness, "since he no longer is training in his AFSC (Air Force Service Category, or job title) or with his unit of assignment."

Then-Maj. Rufus G. Martin replied Nov. 12, 1973: "Not rated for the period 1 May 72 through 30 Apr 73. Report for this period not available for administrative reasons."

By then, Texas Air National Guard officials had approved Bush's request to leave the guard to attend Harvard Business School; his last days of duty were in July 1973.