WASHINGTON — Defense Secretary Leon E. Panetta has painted such an apocalyptic vision of America’s national security under $500 billion in automatic defense budget cuts that Pentagon officials said Tuesday 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 — the United States still has more than any other country — 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.”