By Caren Bohan

WASHINGTON (Reuters) - President George W. Bush apologized to wounded U.S. troops who endured dilapidated conditions and bureaucratic delays as he toured Walter Reed Army Medical Center, the flagship military hospital.

Bush, in his first visit to Walter Reed since a scandal over health care there erupted in February, met with some patients who had previously been at the outpatient building where the worst conditions were found.

"I was disturbed by their accounts of what went wrong," Bush said. "I apologize for what they went through and we're going to fix the problem."

A Washington Post article that found soldiers wounded in the Iraq and Afghanistan wars were living in a run-down building that was infested with mice, mold and cockroaches. Many soldiers also struggled with red tape in trying to get treatment.

"The problems at Walter Reed were caused by bureaucratic and administrative failures," Bush said.

The dilapidated building has since been closed and the patients have been moved to other facilities at Walter Reed.

The reports on Walter Reed provoked an outcry on Capitol Hill. Three senior military officers have lost their jobs and Bush has ordered a wide-ranging review of all U.S. veterans facilities. More than 24,000 soldiers have been wounded and more than 3,600 killed in the two wars.

Bush toured a physical therapy unit where soldiers, many of whom had lost limbs, were exercising on elliptical machines and weight presses.

Bush has often visited wounded soldiers and their families at Walter Reed and at other military hospitals but those meetings were almost always private.

Democrats called Bush's visit a "photo op" and urged him to back off his threat to veto a war-spending bill that has $4.3 billion in health aid for returning soldiers.

Bush plans to reject the Democratic-crafted measure because it includes timelines for troop withdrawals from Iraq. He has cited the need to support the troops in calling on Congress to urgently send hima clean bill.

Sen. Barack Obama, an Illinois Democrat who is also seeking his party's 2008 presidential nomination, accused Bush of being slow to tackle problems with veterans health care.

"The problems plaguing our military hospital system will not be solved with a photo op," Obama said in a statement. "Our military hospital system is in a state of crisis. Delays and rhetorical band-aids will not move us closer to a solution."