President Barack Obama, accompanied by Defense Secretary Leon Panetta, left, Army Chief of Staff Gen. Raymond T. Odierno, and other officials, announced a strategy shift towards Asia and said budget issues will require more restrained use of military force. (Haraz N. Ghanbari/AP)

The U.S. military will steadily shrink the Army and Marine Corps, reduce forces in Europe and probably make further cuts to the nation’s nuclear arsenal, the Obama administration said Thursday in a preview of how it intends to reshape the armed forces after a decade of war.

The downsizing of the Pentagon, prompted by the country’s dire fiscal problems, means that the military will depend more on coalitions with allies and avoid the large-scale counterinsurgency and nation-building operations that have marked the wars in Iraq and Afghanistan.

Instead, the Pentagon will invest more heavily in Special Operations forces, which have a smaller footprint and require less money than conventional units, as well as drone aircraft and cybersecurity, defense officials said. The military will also shift its focus to Asia to counter China’s rising influence and North Korea’s unpredictability. Despite the end of the Iraq war, administration officials said they would keep a large presence in the Middle East, where tensions with Iran are worsening.

The strategy review was unveiled by President Obama in a rare visit to the Pentagon, where he was flanked by Defense Secretary Leon E. Panetta, the Joint Chiefs and other officials who sought to project an image of undiminished military power even as they gird for an era of austerity that will necessitate a more restrained use of military force and more modest foreign policy goals.

“Yes, our military will be leaner, but the world must know the United States is going to maintain our military superiority with armed forces that are agile, flexible and ready for the full range of contingencies and threats,” Obama said.

Obama and Pentagon leaders said their new military strategy, contained in an eight-page document, will guide wrenching decisions on defense cutbacks. Details will be made public in the next few weeks as the White House finalizes its proposed federal budget for the next fiscal year.

In a deficit-reduction deal reached with Congress in August, the White House agreed to cut projected defense spending over the next 10 years by about $480 billion, or about 8 percent of what the Pentagon had planned on.

Although Pentagon officials have portrayed those cuts as painful, Obama said the defense budget is still expected to increase slightly — at about the rate of inflation — each year for the next decade.

“I firmly believe, and I think the American people understand, that we can keep our military strong and our nation secure with a defense budget that continues to be larger than roughly the next 10 countries combined,” he said.

What really worries Pentagon leaders, however, is that their fiscal problems might well be about to get worse. Under a separate deal with Congress, an additional $500 billion in defense cutbacks will be triggered unless lawmakers can agree on an alternative plan to trim the deficit by the end of the year.

Gordon Adams, a former national security budget official in the Clinton administration, predicted that lawmakers would find a way to avoid that trigger, which Panetta has called a “doomsday” scenario for the Defense Department.

But Adams said other defense cutbacks are likely as Congress tries to find ways to improve the national balance sheet. “That’s inevitable,” he said. “Only one shoe has fallen here. There’s another shoe to fall.”

Some Republican lawmakers ripped Obama’s military strategy, saying it would weaken America’s standing in the world. “This is a lead-from-behind strategy for a left-behind America,” said Rep. Howard P. “Buck” McKeon (Calif.), chairman of the House Armed Services Committee.

Republican contenders to run against Obama in November have also heightened their criticism of his national security record. But with the GOP reluctant to endorse higher taxes, some Republican candidates and legislators have said the defense budget should not be exempt from further cuts.

In contrast to past Pentagon reviews, the new strategy offers some clear guidance to the military services about which missions to eliminate and which areas of the sprawling defense establishment to scale back.

The approach recognizes that military and intelligence agencies will have to continue the battle against al-Qaeda and other global terrorist groups. But instead of using conventional Army and Marine Corps forces in long counterinsurgency wars, the Obama administration wants to focus more heavily on “tailored capabilities appropriate for counter-terrorism and irregular warfare.”

The strategy does not formally reject the idea that U.S. military forces will be called on in the future to bring order to fractured societies in the developing world. But it suggests that any stability operations similar to those conducted during the past decade in Iraq and Afghanistan will be of short duration and have far more limited goals.

“Nowhere in the document does it say we’re not going to fight land wars. It doesn’t say we’re never going to do stability operations,” said Army Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff. “It’s a matter of scope and scale, time, risk, reversibility.”

Obama insisted that any cuts to the military will not come at the expense of an expanding U.S. presence in Asia, which he dubbed a “critical region.” To pay for those increases, the strategy suggests a need for significant cuts to the size of U.S. military ground forces in Europe, which has been a major Army operation for decades.

European allies, many confronting even more austere times than the United States, have been bracing for a reduction in the 80,000 U.S. military personnel stationed in Europe.

British Defense Secretary Philip Hammond, who visited Washington on Thursday to meet with Panetta and other U.S. officials, said NATO countries will have to do more to pool their diminishing resources.

“We Europeans need to reassure the U.S. that we are serious about defense,” Hammond said in a speech to the Atlantic Council, a transatlantic think tank. “The U.S. need to reassure Europe that you are not going away.”

Top Obama administration officials revealed few details about which weapons programs will be cut and how many troops will be pared.

In the past decade, the Army has grown to about 570,000 troops, up from 482,000 before the wars in Iraq and Afghanistan. Current plans call for the Army to shrink to about 520,000 troops, although senior Army leaders said they expect their forces to be cut further.

The strategy document also foreshadows cutbacks in the size of the U.S. nuclear arsenal, stating: “It is possible that our deterrence goals can be achieved with a smaller nuclear force.”

Defense officials declined to elaborate, but they said they would offer more information when they release next year’s proposed Pentagon budget.

The United States has about 5,000 nuclear warheads in its arsenal. The New START nuclear pact with Russia, ratified by the Senate in December 2010, mandates that each country reduce the number of nuclear weapons deployed on long-range missiles and bombers to 1,550.

The Obama administration also signaled the scaling back of another Cold War strategic construct. For decades, the military has adhered to a policy of maintaining enough forces to fight two regional wars at once. The new strategy commits the Pentagon to being able to fight a single large-scale war while retaining enough forces to deter or impose “unacceptable costs on an opportunistic aggressor in a second region.”

The strategy also cites the need for the Pentagon to trim personnel costs by reducing the amount of money the department spends on pay, health care and other benefits. Cutting those costs has been a major goal of the Pentagon for most of the past decade. But the effort has consistently run into a buzz saw on Capitol Hill, where lawmakers have resisted even small reductions to military pay and benefits.