WASHINGTON – Under fire from Congress, the Defense Department Friday promised to release by next Tuesday afternoon detailed material backing up its recommendations to shut down about 180 military installations across the country.

And because parts of the report are classified, the Pentagon said lawmakers and staff with security clearances will be able to review all the data at a secure location in northern Virginia.

The announcement comes the same day that Anthony Principi, the chairman of the commission charged with reviewing the proposed base closings, said the panel can’t do its job unless the material is released promptly.

“It needs to be soon,” Principi said as he left a Capitol Hill meeting with officials from Maine and New Hampshire. “We cannot make informed decisions without the data, and that’s critical to our work.”

Lawmakers hope to use the information to persuade the panel to remove bases from the hit list.

Sen. Olympia Snowe, R-Maine, said support is growing for legislation that would postpone the base closing process by one day for every day the Defense Department misses its May 23 deadline to provide the data to the commission.

“This is the typical stonewalling and obfuscation by the Defense Department,” Snowe said. “We should reset the clock.”

Legislators at the meeting “in no uncertain terms demanded that the data be made available,” said Sen. John E. Sununu, R-N.H.

Phil Grone, the deputy undersecretary of defense for installations and environment, met with key Congress members Friday to explain why the data release is taking so long, and how lawmakers will be able to review the material.

In a plan laid out by Grone, the entire database will be available to lawmakers by the end of the workday Tuesday. And by June 4, all unclassified material will be available to the public.

The governors of Maine and New Hampshire as well as all four senators and members of the House were at the closed meeting, which lasted about an hour.

Delegation members said they were pleased with the meeting and that Principi was impressed with some of the information they delivered.

“He pledged that he is not going to be a rubber stamp for the Pentagon,” said Sen. Susan Collins, R-Maine.

Maine Gov. John Baldacci said he stressed the economic impact the closings will have, and predicted the enormity of the cuts proposed in New England will galvanize support to save the bases.

The Pentagon recommended closing the Portsmouth Naval Shipyard and removing aircraft and slashing personnel at Brunswick Naval Air Station. It also proposed closing a Defense Finance and Accounting center at the former Loring Air Force Base in Limestone.

Baldacci said the cuts would deliver a devastating blow to the economy and cost 17,000 jobs.

Commission members began visiting bases this week. The base visits, Principi said, are valuable to learn more about the effects on the communities and the bases’ military value. The commission must forward its recommendations to President Bush in September.

Associated Press writer Beverley Wang in Concord, N.H., contributed to this report.