For the first time in more than a decade defined by costly wars in Afghanistan and Iraq, the Pentagon announced plans Thursday to freeze its ballooning budget, forcing the military to shrink the Army and Marines and increase health care premiums for troops and their families. The Pentagon says it can stop asking for annual budget increases in 2015, adjusting its spending only for inflation. The last time the Pentagon's budget went down was in 1998.

The plan is aimed at helping the nation whittle away at its massive deficit. But the proposal, which requires $78 billion in spending cuts and relies on another $100 billion in cost-saving moves to cover urgent requirements, is tied to two assumptions: that the war in Afghanistan will end on time and that Congress will agree to plans to cancel popular job-making programs and charge retired military families more for health care.

Defense Secretary Robert Gates acknowledged that projections about what the world will look like so far in the future have a troubled track record.

But the Defense Department is "not exempt" from belt-tightening just because of its charge to defend the nation, he said.

"Looking five years into the future is through a pretty cloudy crystal ball," Gates said. "Any number of these decisions could be reversed."

Although it took Gates more than 30 minutes to read an explanation of the reductions, he called the proposals modest and realistic.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said he thinks the Afghanistan war will shrink as planned in 2014, when the United States and its allies want to hand over control of the country's security to the Afghan government.

"There's certainly some risk there, but we think it's acceptable risk right now," Mullen said.

Almost immediately the proposal ran into opposition in Congress, including Republicans who say President Barack Obama is short-changing the military.

"I'm not happy," said Rep. Buck McKeon, who as chairman of the House Armed Services Committee helps oversee the military budget.

"This is a dramatic shift for a nation at war and a dangerous signal from the commander-in-chief," McKeon, R-Calif., added.

In the meantime, many newly elected Tea Party activists and anti-war Democrats have said the Defense Department isn't doing enough to scale back its mammoth half-trillion dollar annual budgets.

The Defense Department represents the largest portion of the federal government's discretionary budget.

"We have nearly doubled our military budget in the past 10 years," Sen. Rand Paul, R-Ky., told his local newspaper, The Courier-Journal, this week.

"To avoid bankruptcy, we will have to evaluate all spending — from food stamps to foreign aid to foreign wars," Paul said.

Gates said his proposal falls between the extremes of those who want to slash the Pentagon budget and those who want to expand it.

"My view is we've got it about right," he said.

The plan calls for $553 billion to be spent in 2012 on annual defense programs such as weapons modernization and troop pay. The amount, which does not include war spending, is $13 billion less than the Pentagon wanted, but still represents 3 percent growth after inflation.

But the rate of increase of spending would gradually slow before halting in 2015 and 2016. The only increase in those budgets would reflect the inflation rate. Gates estimates doing this would cost the military about $78 billion.

To help offset the cost, Gates said the Pentagon would reduce the number of soldiers in the Army by 27,000 and trim the Marines by 20,000, saving as much as $6 billion.

The plan assumes the U.S. will be able to substantially reduce its troop levels in Afghanistan in the next few years. While Obama has called for troop reductions to begin this July, the Afghan government has said it probably won't be able to take control of its government until the end of 2014.

The cuts could meet resistance in Congress, where lawmakers repeatedly have called for increasing the number of ground troops to ensure they aren't subject to lengthy deployments.

The plan also assumes that Congress will agree to some $7 billion in health care reforms for military families. Gates has long argued that benefits provided under the military system, known as TRICARE, are too generous. For example, he said, the basic family plan costs only $460 a year — a fee that hasn't been increased since 1995 and would cost $5,000 a year for civilian federal workers.

Gates said he wants military retirees under the age of 65 to pay "modest" increases to fees.

Similar Pentagon spending reform plans have been defeated in the past, with lawmakers fiercely protective of any program that benefits troops.

Other savings to cover the $78 billion would be found by freezing civilian pay, cutting the size of the general officer corps and other bureaucratic steps.

Separately, about $100 billion in savings has been found in the services' five-year budgets. However, Gates said, the services will mostly be allowed to reinvest that money into programs they want, including weapon modernization.

For example, the Navy and Marine Corps found ways to save about $34 billion, including by canceling a $14 billion program to develop the Expeditionary Fighting Vehicle. Gates said that money will be used to buy additional ships, F-18 jets and new electronic jammers.

That proposal also drew rebukes from lawmakers who feared a loss of jobs in their states.

"I'm willing to work with Secretary Gates and the president to cut wasteful defense spending, but cutting the budget on the backs of Ohio's workers is unacceptable," said Sen. Sherrod Brown, D-Ohio.