Top Republicans on the Senate Armed Services Committee are pressing Defense Secretary Leon Panetta to spell out the "devastating effects" to the military if a special bipartisan panel fails to produce a deficit-cutting plan and nearly $1 trillion in defense cuts kick in.

Sens. John McCain of Arizona and Lindsey Graham of South Carolina sent a letter to the Pentagon chief late Thursday saying Congress and the American people need to know specifics of the scale and scope of such reductions. The two lawmakers also met this week to prepare legislation that would undo deeper defense cuts.

The Pentagon is facing some $450 billion in cuts in projected spending over the next 10 years. But if the special bipartisan panel tasked with finding at least $1.2 trillion in deficit cuts by Nov. 23 fails to produce a plan, then automatic, across-the-board cuts would take effect beginning in January 2013. The military would be looking at more than $500 billion in cuts on top of the current reductions.

Panetta has referred to that process as the "doomsday mechanism" and has said it would have "devastating effects" on the Pentagon and on national security.

"We could not agree more and fear the results ... will be a hollow military," McCain and Graham wrote. Missing from the apocalyptic descriptions, they said, "is a frank and honest assessment describing in concrete terms what defense spending cuts of this magnitude would entail."

McCain has said repeatedly he would fight additional defense cuts beyond the half trillion set in motion by the debt accord reached by President Barack Obama and congressional Republicans last summer.

"If there is a failure on the part of the supercommittee, we will be amongst the first on the floor to nullify that provision," McCain told reporters last month. "Congress is not bound by this. It's something we passed. We can reverse it."

McCain and Graham are working on legislation that would undo the automatic defense cuts and instead impose a 5 percent across-the-board reduction in government spending combined with a 10 percent cut in pay for members of Congress. Undoing the defense cuts, however, could add tens of billions of dollars to the deficit.