SAN DIEGO — Thousands of U.S. troops are being barred from overseas duty because they are so deep in debt they are considered security risks, according to an Associated Press review of military records.

The number of troops held back has climbed dramatically in the past few years. And while they appear to represent a very small percentage of all U.S. military personnel, the increase is occurring at a time when the armed forces are stretched thin by the wars in Iraq and Afghanistan.

"We are seeing an alarming trend in degrading financial health," said Navy Capt. Mark D. Patton, commanding officer at San Diego's Naval Base Point Loma.

The Pentagon contends financial problems can distract personnel from their duties or make them vulnerable to bribery and treason. As a result, those who fall heavily into debt can be stripped of the security clearances they need to go overseas.

While the number of revoked clearances has surged since the beginning of the Iraq war, military officials say there is no evidence that service members are deliberately running up debts to stay out of harm's way.

Officials also say the increase has not undermined the military's fighting ability, though some say it has complicated the job of assembling some of the units needed in Iraq and Afghanistan.

The problem is attributed to a lack of financial smarts among recruits; reckless spending among those exhilarated to make it home alive from a tour of duty; and the profusion of "payday lenders" — businesses that allow military personnel to borrow against their next paycheck at extremely high interest rates.

The debt problems persist despite crackdowns on payday lenders and the financial counseling the Pentagon routinely offers to the troops.

Data supplied to the AP by the Navy, Marines and Air Force show that the number of clearances revoked for financial reasons rose every year between 2002 and 2005, climbing ninefold from 284 at the start of the period to 2,654 last year. Partial numbers from this year suggest the trend continues.

More than 6,300 troops in the three branches lost their clearances during that four-year period. Roughly 900,000 people are serving in the three branches, though not all need clearances.

The figures gathered by the AP represent just a piece of the problem, because the Army — which employs an additional 500,000 people and accounts for the vast majority of the 160,000 U.S. troops in Iraq and Afghanistan — rejected repeated requests over the past month to supply its data, saying such information is confidential.

A key reason the military revokes clearances on financial grounds is the fear that soldiers in debt might be tempted to sell secrets or equipment to the enemy.

Also, "when they are over there fighting, we like them to have their heads in the game," said Maj. Gen. Michael Lehnert, commander of Marine Corps bases in the western United States. "We like to have them ... not worrying about whether or not they are going to be able to make the mortgage payment or car payment."