"We're trying to minimize the harm to defense but we need to take some actions now to avoid larger harm later," Deputy Defense Secretary Ash Carter said Friday.
Carter said the US military had to start slowing its spending rate given the threat of automatic budget cuts that are due to kick in after March 1, if Congress fails to break a political stalemate.
"This is what we're doing now to slow our spend rate," he said.
The Pentagon would face roughly $50 billion in reductions and given the March 1 deadline, would have only five months left in the current fiscal year to absorb them, he told AFP and several other news outlets.
The Pentagon's 46,000 temporary and contract employees are "all now subject to release," he said.
The workers would either be laid off or not have their contracts renewed, except for those performing jobs deemed vital for the war or core missions, he said. The department has already announced a freeze on the hiring of civilians.
To brace for possible cuts, Carter said the Pentagon also was deferring maintenance of military equipment and bases.
In addition to the potential automatic budget cuts, the Pentagon is also under financial pressure because Congress had yet to approve the department's proposed budget for 2013.
The military has been forced to operate at slightly lower funding levels set for fiscal year 2012. As a result, plans to increase funds for the maintenance of bases and equipment have been derailed, he said.
To prepare for the worst case budget scenario, maintenance on various military hardware -- including naval ships, aircraft and vehicles -- has had to be postponed or canceled, he said.
"For example, the navy is going to cancel maintenance of 30 ships that is scheduled for the third and fourth quarters of this year," Carter said.
And "the Air Force is only entering into short-term contracts for supplies," he said.
The Pentagon's number two said he had asked the armed services to produce detailed plans by February 1 to outline how they will cut short-term spending before the drastic "fiscal cliff" reductions enter into force on March 1.
And Carter ordered the armed services to produce long-term plans by February 8 on how they would absorb the billions in automatic cuts.
The Pentagon already has had to scale back projected defense spending over the next 10 years by about $487 billion under the Budget Control Act adopted in 2011.
Congress created the automatic "sequestration" mechanism to force lawmakers to come up with a compromise deal and avoid the sweeping reductions.