Washington - Defense Department officials warned a House panel Thursday that if Congress does not approve the Obama administration's proposal for two new rounds of base closings, the Pentagon will use existing authority to close some facilities.

"Strategic and fiscal imperatives leave the department no alternative - we must close and realign military bases here in the United States," Dorothy Robyn, deputy undersecretary of defense for installations and environment, told the House Armed Services readiness subcommittee at a hearing on the request for more Base Realignment and Closure (BRAC) rounds.

"If Congress does not authorize additional BRAC rounds . . . the department will be forced to use its existing authorities to begin to support our new defense strategy," Robyn said.

She said that the Defense Department has more than 300,000 buildings and 2.2 billion square feet of space, which is "more than Wal-Mart."

"We are focused on getting rid of capacity we don't need so we can use the resources elsewhere," Robyn said.

The proposal came under sharp bipartisan attack from panel members who criticized the administration for making the plan without providing any estimates of cost savings or other details.

"We need a lot more facts before we pass on another round of BRAC," said Rep. J. Randy Forbes, R-Va., chairman of the readiness subcommittee.

"I'm as concerned as other members in not knowing the cost," said Rep. Silvestre Reyes (D-Tex.). "We're moving in the dark with a request for two BRACs."

Some members also argued that making further cuts ignored looming threats to U.S. security, in particular with U.S. troops still in Afghanistan and as the United States and other world powers press Iran over alleged research into nuclear weapons.

The Obama administration is "losing sight of the fact we're still at war," Rep. Mike D. Rogers (R-Ala.) said. "We could be in Iran in a heartbeat."

Robyn said that the Pentagon has only begun "initial preparatory work" for a new BRAC, including making inventories of property and examining whether analytical tools for evaluating which facilities to close need to be updated.