Defense Secretary Leon Panetta on Thursday signaled that the Pentagon will push hard against future spending cuts, saying that up to $500 billion in cuts that could come later this year would be a “doomsday mechanism” that would endanger national security.

“We are already taking our share of the discretionary cuts as part of this debt ceiling deal, and those are going to be tough enough,” Panetta said at his first press conference since taking office July 1.