The Pentagon got its last chance Saturday to try to ease the concerns of a commission reviewing Defense Secretary Donald H. Rumsfeld's proposal to close or scale back hundreds of U.S. military bases.

"Change is hard, and we fully appreciate its impact," said Michael Wynne (search), who led the Pentagon team that drew up the plan.

However, Wynne said, it's also necessary. Closing some bases and shrinking others frees up money to allow the U.S. military to improve its combat capabilities, he said.

In a rare weekend hearing, Defense Department (search) officials told the nine-member commission that they did not overestimate savings from the plan and that the proposal would strengthen, not harm, the country's security.

The hearing was convened just days before the commission holds a series of meetings to vote on whether to accept or reject each part of Rumsfeld's plan.

Anthony Principi (search), the commission's chairman, has pledged not to "rubber-stamp" the proposal, and on Saturday he told Pentagon officials that significant questions remain just days before the commission's final deliberations.

"Will the claimed savings actually be realized? Are costs understated?" Principi asked in his opening remarks.

The commission has questioned the Pentagon's claim that it will save $48.8 billion over 20 years if the proposal is enacted. It has pointed to a report by the Government Accountability Office that found upfront costs will total $24 billion and disputed the Pentagon's projected savings.

Pentagon officials stood by their numbers.

Also a concern is the impact of the Air Force's restructuring of the Air National Guard (search) on homeland security. It would close or downsize nearly 30 facilities where Air Guard units are stationed and leave units with no planes to fly in many of those cases. The Air Force says those units would get new, non-flying missions. State governors, and their adjutants general who oversee Guard forces, oppose the plan.

"Has the chasm gulf separating the Air Force from the Air National Guard been bridged?" Principi asked.

"We don't consider disagreements with a few adjutant generals out there in the states as a rift between the Air Force and the National Guard," Gen. John Jumper, the Air Force's chief of staff, told the commission. "I don't think there is a chasm out there that has to be bridged."

The commission also worries that the recommendations will leave the Northeast unprotected. On the Pentagon's chopping block are two major New England bases — the submarine base at Groton, Conn., and the Portsmouth Naval Shipyard in Kittery, Maine. Forces at the Naval Air Station in Brunswick, Maine, would be drastically reduced.

"No single installation was considered in a vacuum," Adm. Robert Willard, vice chief of naval operations, told the panel. He said military value, as well as savings, were considered to ensure the best defense of the country.

In May, Rumsfeld proposed shutting down or at least reducing forces at 62 of the country's largest base and hundreds of smaller military facilities to save money and streamline the Army, Navy, Air Force and Marine Corps.

Over the past few months, commissioners and staff have made 182 visits to 173 installations and conducted 35 hearings. The commission has received more than 80,000 electronic messages and more than a half-million pieces of paper mail from those commenting on the process.

At least some changes to the proposal are likely. Previous commissions — in 1988, 1991, 1993 and 1995 — changed about 15 percent of what the Pentagon proposed, and analysts expect history to repeat itself this year.