WASHINGTON — Defense Secretary Chuck Hagel has proposed cuts in military spending that include further reductions in troop strength and force structure in every military service in the coming year as part of an effort to prioritize U.S. strategic interests in the face of reduced resources after more than a decade of war.

At a Pentagon news conference Monday detailing President Barack Obama's proposed Pentagon budget for fiscal year 2015, Hagel called the reductions — including shrinking the Army to its smallest size since before World War II and eliminating an entire fleet of Air Force fighter planes — "difficult choices" that will change defense institutions for years to come, but designed to leave the military capable of fulfilling U.S. defense strategy and defending the homeland against strategic threats.

Under a Pentagon budget that will shrink by more than $75 billion over the next two years — with deeper cuts expected if sequestration returns in fiscal year 2016 — Hagel and other senior defense and military officials acknowledged that some of the budget choices will create additional risks in certain areas.

Some of that risk, Hagel said, is associated with a sharp drawdown in the size of the Army, which the proposed budget calls for reducing to as low as 440,000 active duty soldiers from the current size of 520,000, while ensuring the force remains well trained and equipped.

The cuts assume the United States no longer becomes involved in large, prolonged stability operations overseas on the scale of Iraq and Afghanistan. "An Army of this size is larger than required to meet the demands of our defense strategy," Hagel said. "It is also larger than we can afford to modernize and keep ready." But he said the smaller force still would be capable of decisively defeating aggression in one major war "while also defending the homeland and supporting air and naval forces engaged in another theater against an adversary."

The budget request calls for special operations forces to grow by nearly 4,000 personnel, bringing the total to 69,700, a reflection of the asymmetrical threats the nation is likely to face in the future, Hagel said.

The restructuring and downsizing are in line with a two-year budget agreement that the president and Congress worked out in December, which limits defense spending to $496 billion. But Hagel warned today that if the budget for fiscal year 2016 returns to the steep, automatic spending cuts imposed by sequestration, "we would be gambling that our military will not be required to respond to multiple major contingencies at the same time."

Asked to define that increased risk, a senior Defense Department official expressed it simply. "If the force is smaller, there's less margin for error," the official said. "Let's face it — things are pretty uncertain out there."

The proposed budget also envisions a 5-percent reduction in the Army National Guard and Army Reserve. "While it is true that reserve units are less expensive when they are not mobilized, our analysis shows that a reserve unit is roughly the same cost as an active duty unit when mobilized and deployed," Hagel said.

In addition, the Army Guard's Apache attack helicopters would be transferred to the active force, while Black Hawk helicopters would be transferred to the National Guard, part of a broader realignment of Army aviation designed to modernize the fleet and increase capability.

Within the Air Force, the defense budget calls for saving $3.5 billion by retiring the A-10 fleet and replacing it with the F-35 by the early 2020s.

"The A-10 is a 40-year old, single-purpose airplane originally designed to kill enemy tanks on a Cold War battlefield," Hagel said. "It cannot survive or operate effectively where there are more advanced aircraft or air defenses." In addition, the service also will retire the 50 year-old U-2 surveillance plane in favor of the unmanned Global Hawk.

Hagel warned that much deeper cuts in Air Force structure and modernization will be necessary if sequestration is not avoided in 2016.

Among other proposals in the budget request:

• The Army will cancel the Ground Combat Vehicle program;

• The Navy would be able to maintain 11 carrier strike groups, but any steep future cuts could require mothballing the aircraft carrier USS George Washington;

• Half of the Navy's cruiser fleet, 11 ships, will be placed in reduced operating status while they are modernized and given a longer lifespan;

• The Navy will continue buying two destroyers and attack submarines per year;

• The Marine Corps will draw down from about 190,000 to 182,000, but would have to shrink further if sequestration returns;

• An additional 900 Marines will be devoted to securing U.S. embassies; and

• The Defense Department is asking Congress for another round of base closings and realignments in 2017.

Hagel said most of the recommendations in the budget were accepted by senior military officers. Addressing reporters alongside him, Army Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff, said the spending plan reflects a balancing of the military while ensuring it remains the world's finest.

"It reflects in real terms how we're reducing our cost and making sure the force is in the right balance," Dempsey said.

Dempsey and Hagel will testify on the budget before Congress next week. Lawmakers will have the final say on spending decisions.

"This is the first time in 13 years we will be presenting a budget to Congress that is not a war footing budget," Hagel noted.