The Pentagon will begin taking steps to freeze civilian hiring, delay some contract awards and curtail some maintenance to prepare for drastic budget cuts if Congress can't reach an agreement on a final spending plan, Defense Secretary Leon Panetta said Thursday.

Speaking to reporters, Panetta said that department officials must also develop detailed plans to implement unpaid furloughs for civilian personnel. The furloughs would kick in if the automatic cuts are triggered.

But Panetta said he has asked defense leaders to ensure that any initial moves they make now should be reversible if at all possible, and they must minimize harmful effects on military readiness.

"The simple fact is that this fiscal uncertainty has become a serious threat to our national security," Panetta said during a Pentagon press conference. "We really have no choice but to prepare for the worst."

The Pentagon is facing a spending reduction of nearly $500 billion over a decade. An additional $110 billion in automatic spending cuts to military and domestic programs will take effect in early March if no agreement is reached.

At the same time, Panetta and Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, noted that Congress has not passed the 2013 defense department budget proposed by the Pentagon last year, and has instead just approved spending equal to the 2012 fiscal year levels. As a result, Panetta said if Congress fails to pass a new budget or avoid the automatic cuts the Pentagon will have to find an almost immediate $40 billion in savings.

And Dempsey said overall the department would have to absorb as much as $52 billion in cuts to planned spending by the end of the fiscal year on Sept. 30.

In order to protect the troops still fighting in Afghanistan, Dempsey said the effect on the rest of the force would be devastating.

"Operations, maintenance and training will be gutted. We'll ground aircraft, return ships to port, and sharply curtail training across the force," Dempsey said. "We'll be unable to reset the force following a decade of war. Our readiness will begin to erode. Within months, we'll be less prepared. Within a year, we'll be unprepared."

He stressed, however, that he will not shortchange troops in combat or wounded warriors and their families.

Panetta's guidance was laid out in a four-page memo to department heads that outlined the "near-term actions" they should take including potentially firing any temporary hires, informing some contract employees that they will not be renewed, curtail travel, training, conferences, and spending on supplies, and cut money from base operations.

He said that by Feb. 15, officials must cancel ship, aviation and depot maintenance for the third and fourth quarters

Panetta, who has consistently been harshly critical of Congress' impasse on the budget, said he understands that the politics are difficult, but lawmakers in Washington need to have the same courage as the military troops fighting on the warfront. A former budget director in the Clinton administration, when afiscal impasse forced lawmakers to briefly shut down the federal government, Panetta said the political tenor in town has worsened.

"When we dealt with Reagan as president, and when we dealt with Bush as president, it was a Democratic Congress. The (House) speakers at the time really felt that if we could work out agreements with the president, that even though a Republican president would benefit, a Democratic Congress would benefit, as well, by governing the nation," recalled Panetta. "For whatever reason, that concept has been lost."

Now, he said, "I think that there's an attitude that governing isn't necessarily good politics, that gridlock and confrontation is good politics. And I think we pay a price for that."