If the Joint Select Committee on Deficit Reduction, the congressional supercommittee charged with finding ways to cut federal spending, fails to reach consensus on reducing the debt, the U.S. government will be forced to make mandatory cuts.
Panetta said the automatic cuts -- known as sequestration -- that would go into effect Jan. 1, 2013 would amount to a 23 percent across-the-board cut in defense programs.
In a letter Monday to Sens. John McCain, R-Ariz. and Lindsey Graham, R-S.C., Panetta said the roughly $1 trillion of mandatory cuts to defense would curtail shipbuilding and construction contracts and result in the furlough of civilian personnel and contractors.
"The impacts of these cuts would be devastating," Panetta said in the letter. "Rough estimates suggest after ten years of these cuts, we would have the smallest ground force since 1940, the smallest number of ships since 1915, and the smallest Air Force in its history."
McCain and Graham, in a joint statement, said the consequence of a sequester on the Defense Department would "set off a swift decline of the United States as the world's leading military power."
"We are staunchly opposed to this draconian action. This is not an outcome that we can live with, and it is certainly not one that we should impose on ourselves. The sequester is a threat to the national security interests of the United States, and it should not be allowed to occur."