WASHINGTON >> The top members of the Senate Armed Services Committee voiced concern Tuesday over an imminent U.S.-Japan agreement on reorganizing U.S. forces based on the southern island of Okinawa. More than 2,500 Marines would come to Hawaii under the plan.

Chairman Carl Levin, ranking Republican John McCain and Democrat Jim Webb have written to Defense Secretary Leon Panetta cautioning that no agreement should be considered final without congressional approval.

The U.S. and Japan agreed in February to proceed with the transfer of 8,000 U.S. troops from Okinawa, home to more than half the 50,000 U.S. forces in Japan. U

The transfer has been in limbo for years because it was linked to the closure and replacement of the strategically important U.S. Marine base that Okinawans fiercely oppose, and building a new facility in a less congested part of the island. The allies kept the overall plan, but agreed to move ahead with the troop transfers to Guam and other destinations before completing the new base.

Panetta discussed the issue by phone with his Japanese counterpart on Monday, and a Pentagon statement said the specifics would be announced in the very near future.

Japanese Prime Minister Noda is visiting Washington next week.

Details of the new agreement emerged in the Japanese press Tuesday, outlining how several military bases and facilities on Okinawa would return to Japanese control in stages.

"We are mindful of the turbulence that this issue has brought to U.S.-Japan relations and to the domestic political climate in Japan and on Okinawa," the senators wrote in their letter. "It is essential that we get these important decisions right, and that they be guided by sound strategic concepts and fiscally sustainable plans."

The senators have criticized the original reorganization plans as impractical and costly, and included a provision in the defense budget for 2012 to make progress contingent on the Defense Department’s first allowing an independent review.

They said in a statement they have "serious questions that have not been fully addressed regarding the emerging agreement." They specified worries over cost estimates, force management and how the plans would support broader U.S. strategy in the region.

Washington is under pressure to make the most of its resources as budget cuts loom. At the same time, the Obama administration wants to enhance the U.S. military presence in the Asia-Pacific to counter China’s rapid military build-up.