WASHINGTON -- The Pentagon's $2 billion cost estimate for disposal of chemical weapons at Kentucky's Blue Grass Army Depot is outdated and flawed and must be thrown out, Kentucky's two senators said yesterday.

Sens. Mitch McConnell and Jim Bunning, both Republicans, said in a letter to the Defense Department that the estimate could stop engineers from developing a workable and safe design for a disposal plant.

The Pentagon "has painted itself into a corner by unnecessarily placing a cap on the cleanup costs at Blue Grass," McConnell said in a statement released with the letter to Defense Undersecretary Kenneth Krieg .

"I will never allow misguided cost savings to come at the expense of the safety of Kentuckians," he said.

Navy Lt. Cmdr. Joe Carpenter, a Pentagon spokesman, said he could not answer questions about the letter since it had just been received.

Carpenter said the chemical weapons disposal program is conducting an analysis for Blue Grass and a similar plant in Colorado "that will meet cost, schedule and performance criteria."

But he added: "Safety is a priority for the department and for the program."

Colorado's two senators, Republican Wayne Allard and Democrat Ken Salazar, also signed the letter, which expressed similar concerns about the Pentagon estimate of $1.5 billion for chemical weapons disposal at Pueblo.

Congress did not require estimates for the two facilities, and the 2003 figures that the Pentagon came up with were made "even though no design work had been undertaken at that time," the senators wrote.

Those flawed estimates, the senators said, "are driving critical decisions surrounding current re-design activities" at the two sites.

The Pentagon earlier this year suspended design work on the Kentucky and Colorado plants, citing the cost estimates as justification and saying it needed to concentrate spending on other chemical weapons disposal facilities.

The senators, along with Rep. Ben Chandler, D-6th District, and other House members criticized the Pentagon's move, and ultimately military officials backed down.

Craig Williams, director of the Chemical Weapons Working Group of Berea, Ky., a watchdog group that monitors conditions at Blue Grass, said the senators are right to insist that the Pentagon drop the cost estimates.

Otherwise, he said, if disposal program officials told the Pentagon "the only way we can execute (disposal) safely is at a cost of $2.1 billion, the Pentagon would be able to say, 'Sorry, you've got to go back to the drawing boards,' " Williams said.

"That's the wrong way to do this from a safety standpoint," he said.