Updated

Senators scrambling to head off proposed military base closings in their states are pressing Defense Secretary Donald H. Rumsfeld (search) to release all the data used to decide which facilities to shut down.

Nearly two dozen senators from Maine to Nevada signed a letter to Rumsfeld, saying they need to know how the Pentagon ranked the bases and determined their military value.

In recent hearings, Defense Department officials said military value was a key factor in deciding which bases would close. They described the scores given to some of the bases, but did not yet release backup material.

Members of the Base Closure and Realignment Commission (search) began visiting bases this week, and have scheduled the first regional hearings on the closings for early next month.

"If the Department continues to delay the release of this data, communities adversely impacted by BRAC, and the BRAC commission, will be unable to assess the Department's recommendations in the limited time allotted to them," the senators said in the letter.

Defense Department spokesman Glenn Flood said the material is going to be released, but it is going through security checks because some of the information is classified.

"We realize the concern," he said. "We're working very hard on it."

Base closing commissioners are visiting eight bases in five states next week, including Naval Station New London in Groton, Conn., Portsmouth Naval Shipyard in Kittery, Maine, Otis Air National Guard Base on Cape Cod, Willow Grove Naval Air Station in Pennsylvania, and Fort Monmouth in New Jersey.

At least four members of the panel plan to tour the Groton base, including commission chairman Anthony Principi (search). Two members are heading to the Portsmouth shipyard, and one member -- retired Air Force Gen. Lloyd "Fig" Newton -- will tour Otis.

A plan announced May 13 Rumsfeld would close 33 major bases and downsize 29 others, saving an estimated $48 billion over 20 years.