Defense Secretary Donald H. Rumsfeld predicted Tuesday that a federal commission will endorse "the overwhelming majority" of his proposals to close, shrink or expand hundreds of military bases across the country.

For its part, the nine-member panel has promised not to rubber-stamp the Pentagon chief's plan, and commissioners say changes are likely before they send their final report to President Bush next month.

Previous commissions -- in 1988, 1991, 1993 and 1995 -- altered about 15 percent of whatSept. 11, 2001, era.

"It's not about just trying to get rid of excess capacity. It's actually about trying to reorganize the forces for future challenges," said Loren Thompson, a military analyst with the Lexington Institute, a think tank in Arlington, Va. "That makes the outcome harder to call."

The commission plans to start voting Wednesday on whether to sign off on each part of Rumsfeld's plan, the first such effort in a decade to reconfigure stateside military bases and the most ambitious by far.

The Pentagon proposed closing or consolidating a record 62 major military bases and 775 smaller installations to save $48.8 billion over 20 years, streamline the services and reposition the armed forces to face current threats.

Announced in May, the proposal set off intense lobbying by communities fearful that the closures and downsizings would hurt their economies and by politicians worried they would be blamed by voters for job losses.

Since beginning its work four months ago, commissioners have voiced serious concerns about several parts of Rumsfeld's plan.

The most contentious issues have been the Air Force's proposal to strip aircraft from about two dozen Air National Guard facilities and the Navy's efforts to scale back its forces in New England. They include closing the Portsmouth Naval Shipyard (search) in Maine and Submarine Base New London (search) in Connecticut and sharply reducing forces at Naval Air Station Brunswick (search) in Maine.

Commissioners fear those proposals could hamper homeland security, a contention the Pentagon rejects.

The Air Force's attempt to close Ellsworth Air Force Base (search) in South Dakota, home to freshman Republican Sen. John Thune, has stirred the most political consternation. Thune argued during the 2004 campaign that he -- not Senate Minority Leader Tom Daschle -- would be in a better position to save the facility.

Commissioners also have grappled over one of their own proposals: whether to move the Navy's jet training base at Naval Air Station Oceana (search) in Virginia to Cecil Field (search) in Jacksonville, Fla., which was closed in 1999. The Pentagon opposes the plan, but the commission decided to consider the move because of urban encroachment in Virginia.

"I feel that we made very solid recommendations," Rumsfeld said Tuesday. "I suspect the commission, when all is said and done, will endorse the overwhelming majority of those recommendations."

The commission has set aside four days to decide which bases to spare and which to scrap. It's expected to work at least 14 hours each day, although commissioners are hoping to complete their work before the weekend. Army, Navy and joint-service recommendations will be considered first, followed by the Air Force.

The panel, chaired by former Veterans Affairs Secretary Anthony Principi, must send its final proposal to Bush by Sept. 8. The president can accept the report or order the commission to make changes, a scenario considered unlikely given that his predecessor, President Clinton, was criticized for such intervention in 1995.

If Bush accepts the proposal, it becomes law in about nine weeks unless Congress passes a joint resolution rejecting it. Lawmakers haven't taken that step in any of the previous base-closing rounds.