WASHINGTON (AP) — The United States is footing more of the bill for overseas bases in Germany, Japan and South Korea even as the military reduces the number of American troops in Europe and strategically repositions forces in Asia, a congressional report says.

The exhaustive, yearlong investigation by the Senate Armed Services Committee focused on costs and burden-sharing as the United States spends more than $10 billion a year to back up the U.S. military presence overseas, with 70 percent of the amount expended in the three nations. The figure does not include military personnel costs.

The panel's report, obtained by The Associated Press in advance of its Wednesday release, found the financial contributions by those host countries lagging behind costs or increases in U.S. spending. The report identified inherent problems and missteps in the compensation system as the U.S. returns a growing number of its upgraded facilities on foreign land to the host countries.

The report insisted that the American presence in the countries is vital, especially with bellicose threats from a nuclear North Korea, China's military growth and Germany's partnership with the U.S. in NATO. However, the Pentagon is now facing the pressure of deficit-driven, smaller budgets while looking to scale back or close overseas and U.S. domestic bases.

The cost arrangements with allies have drawn greater congressional scrutiny — and frustration.

"The growth in our share has really been pretty stunning. And I think we've got to stop that direction," Sen. Carl Levin, D-Mich., chairman of the committee, said in an interview. "We cannot carry these greater and greater and greater percentages of the costs of maintaining these facilities. The ones that we give back, we're going to have to be given appropriate consideration for the improvements, and the ones that we keep will have to have a much fairer burden-sharing than has been the case in the last 10 years."

The size of the U.S. force in Germany is expected to drop in the coming year as the Army plans to deactivate one brigade combat team next year and possibly reduce the force even further with a cut of around 2,500 soldiers. Currently, the U.S. has 48,000 active-duty personnel in Germany at a cost of $4 billion.

The amount does not include military personnel costs of $3.9 billion.

The troop reductions — the Army already deactivated one heavy brigade combat team in October 2012 — have resulted in excess military facilities. However, instead of getting cash for the buildings, the U.S. has been negotiating residual value, in-kind payments of services or facilities with a cash value.

Cash payments would be placed in an account and only used for maintenance, repair and environmental restoration. In-kind payments can be directed to military construction.

The committee identified some questionable military construction projects from this arrangement. About $200,000 of residual value, in-kind payments were directed to add sunrooms to senior officer homes in Stuttgart, Germany, in 2007.

"Before the 200-square-foot additions, the homes were each 2,490 square feet, well above DoD's minimum size standard," the report said.

The report found that the U.S. has negotiated the return of more than 100 facilities to Germany since 2005, yet they haven't been included in the residual value settlements between the two countries. Their current value is nearly $1.1 billion.

In South Korea, where there are 28,500 troops, the U.S. plans to move its forces from the Yongsan Garrison in Seoul to Camp Humphreys, about 40 miles south of the capital. The U.S. must provide most of the military family housing and cover the cost, estimated at $7 billion.

In return, South Korea gets prime real estate in downtown Seoul. During the transition, the U.S. will be responsible for maintaining both sites at a considerable cost. The project also calls for a $10 million museum at the newer base.

In January 2009, the two countries signed an agreement on South Korean contributions. The report found that "while the agreement increased South Korean contributions in subsequent years to keep up with inflation, South Korea's contributions have not kept pace with U.S. costs."

The United States' non-personnel costs in South Korea were $1.1 billion last year. U.S. spending in the country was expected to exceed South Korea's contributions by $330 million.

The Americans have about 50,000 troops in Japan, about half stationed on Okinawa. The cost is estimated at $2 billion in non-personnel costs for the U.S.

In 1992, Japan contributed more than $1 billion to the facility improvement program, an amount that has dropped to $200 million in recent years. Further complicating the situation, the report found, some 20 percent of that amount is reserved for Japanese projects, often ones requested by local communities.

For nearly two decades the closure of Marine Corps Air Station Futenma and the construction of a replacement facility in northern Okinawa have been in the works. In hopes that the new facility was imminent, repairs and other work at Futenma remained undone and many of its 50-year-old-plus facilities show their age.

Only a few projects were financed at an installation that been "closing since 1996," the report said.

Last month, the committee approved the report by voice vote.