Defense Secretary Leon E. Panetta has painted such an apocalyptic vision of America’s national security under $500 billion in military budget cuts triggered by the failure of a congressional deficit panel, that Pentagon officials said Tuesday that they were pushing back at Congress and not even planning for the spending reductions, which are to take effect in January 2013.

But independent military budget analysts described the cuts, which would bring the Pentagon base budget back to 2007 levels, as agonizing but manageable.

The analysts, who have close ties to the Pentagon, expressed amazement that a department that plans for every contingency was not planning for this one. They laid out the possibility of cutbacks to most weapons programs, a further reduction in the size of the Army, large layoffs among the Defense Department’s 700,000 civilian employees and reduced military training time — such as on aircraft like the F- 22 advanced jet fighter, which flies at Mach 2 and costs $ 18,000 an hour to operate, mostly because of the price of fuel.

Other possibilities include cutting the number of aircraft carriers to 10 from 11, as well as increased fees for the military’s generous health care system, changes in military retirement, base closings around the country and delayed maintenance on ships and buildings.

“I’m not suggesting these are smart things to do, necessarily,” said Todd Harrison, a senior fellow at the Center for Strategic and Budgetary Assessments, a military policy and research group in Washington. “But if you had to do it, you could do it.”

The $500 billion in cuts, to be spread out over a decade, would come on top of $450 billion in spending reductions over the next 10 years that the Defense Department and the White House agreed to last summer.

Under the automatic cuts triggered by the committee’s failure, the 2013 Pentagon budget would have to shrink to $472 billion from $525 billion — an 11 percent reduction, or about the size of the Pentagon’s base budget in 2007. (The costs of the wars in Iraq and Afghanistan are not included in the base budgets.)

An 11 percent reduction is nonetheless a cut of $54 billion, which would have to be done in a single year — the real challenge in reducing Pentagon spending this way.

“It’s the abruptness of the cuts, not the depth of the cuts, which makes it hard,” Harrison said.