The deal to avert a US debt default should have little effect on the Pentagon's huge budget in the short term, but leaves the door open to sharp cuts that could force a strategy overhaul, experts say.
Signed into law by President Barack Obama on Tuesday, the compromise lifts cash-strapped Washington's $14.3 trillion debt limit by up to $2.4 trillion, while cutting at least $2.1 trillion in government spending over 10 years.
Defense spending, which has doubled since the 9/11 attacks and accounts for 20 percent of the overall federal budget, is already scheduled to be slashed by $400 billion over 12 years, according to plans unveiled by Obama in April.
But experts say fresh deficit reduction efforts carried out under the new legislation could impose even more drastic cuts on the Pentagon, forcing the Defense Department to make some tough choices.
"That would force a rethink of our defense strategy and possibly our defense posture around the world: where we have troops deployed, how many forces we keep overseas," Todd Harrison of the Center for Strategic and Budgetary Assessments told AFP.
"So it definitely could alter US strategy."
Under the debt deal, the first round of cuts is automatic, totaling $917 billion by 2021. That will translate to $350 billion in military spending cuts, according to the White House.
A special congressional committee has been created to then agree by year's end on the second round of $1.5 trillion in further cuts from all areas.
But if the bipartisan committee fails, then cuts of $1.2 trillion would automatically come into force -- divided evenly between military and non-military spending, meaning the Pentagon could lose another $600 billion.
Experts say that process could be unpredictable, and even the top US military officer, Admiral Mike Mullen, admitted he did not know how the Pentagon would be affected.
"I certainly have an expectation that there will be defense cuts as part of this -- I just don't know what those will be," Mullen said during a visit to Iraq.
"I suspect that we will find out the details here in the next couple of days."
Harrison wrote in a study that the initial $400 billion in defense spending cuts would be possible solely by allowing the military budget to "grow at the rate of inflation from the level of funding enacted in fiscal year 2011."
But the possibility of more deep cuts has spooked fierce backers of military spending in Congress, such as Republican Senator Lindsey Graham and the head of the House Armed Services Committee, Republican Congressman Buck McKeon.
"There is no scenario in the second phase of this proposal that does not turn a debt crisis into a national security crisis," McKeon said in a statement of the compromise deal.
Obama has requested $553 billion in defense spending for 2012, an increase of $5 billion. That does not take into account the $118 billion allocated for the wars in Afghanistan and Iraq.
Andrew Exum, a former US Army officer and expert at the Center for a New American Security, said that while it was "perfectly reasonable" to reassess ground troop numbers and military pension payments, he feared "blind" budget cuts.
"I have no problems with intelligent cuts to the defense budget, though I do have problems with blind swipes of the ax to the defense budget, and I worry we're going to see more of the latter than the former," Exum wrote on his blog.
For Harrison, several budget items could come into play, from the number and types of units in the 1.4-million-strong military to "compensation and benefits" and "major weapons systems."
"All of these variables will be looked at. Some of them are more difficult to do in the short term than others -- bringing down force structure and end strength can take time," Harrison told AFP.
He predicted the equipment budget was "one of the most likely areas to be cut deeply," with plans for the F-35 fighter jet, or Joint Strike Fighter -- the Pentagon's most costly weapons program -- possibly on the chopping block.
"The hard part is to finding what the future threats are and what are the priorities," he said.