WASHINGTON — As much as $60 billion in U.S. funds has been lost to waste and fraud in Iraq and Afghanistan over the past decade through lax oversight of contractors, poor planning and payoffs to warlords and insurgents, an independent panel investigating U.S. wartime spending estimates.

In its final report to Congress, the Commission on Wartime Contracting said schools, medical clinics, barracks, roads and power plants were built with American tax dollars. Much of the waste and fraud could have been avoided with better planning and more aggressive oversight, the report said.

To avoid repeating the mistakes in Iraq and Afghanistan, government agencies should overhaul the way they award and manage contracts in war zones, the commission recommended.

The Associated Press obtained a copy of the commission’s 240-page report in advance of its scheduled public release today.

Created by Congress in 2008, the eight-member commission held more than two dozen hearings, interviewed hundreds of military and civilian officials and traveled multiple times to Iraq and Afghanistan. The panel’s final report is the most comprehensive examination so far of the U.S. dependence on contractors and the government’s ability to manage them in combat areas.

The commission said calculating the exact amount lost through waste and fraud is difficult because there is no commonly accepted methodology for doing so. But using information it has gathered over the past three years, it said at least $31 billion has been lost and the total could be as high as $60 billion. The commission called the estimate “conservative.”

Overall spending on contracts and grants to support U.S. operations in Iraq and Afghanistan is expected to exceed $206 billion through the 2011 budget year.