WASHINGTON – Even as the United States puts fewer resources into Iraq, winds down its ground war in Afghanistan and prepares to make do with a leaner military budget, it faces an array of future threats and must still be prepared to fight several conflicts simultaneously, the Pentagon said Thursday in unveiling its latest defense strategy.

The eight-page document aims to address mounting calls for budget cuts and explain why the Pentagon needs to maintain most of the resources thrown its way over the last decade of war. It concludes that the military must be prepared to conduct one major conventional war and several smaller conflicts at the same time.

The department didn’t say whom the military could be fighting, but it pledged to create a smaller force. To underscore the shift from a decade spent waging two major ground wars, President Obama made a rare appearance at the Pentagon to introduce the strategy, apparently seeking to put his stamp on the cutbacks as he launches his re-election bid.

“The tide of war is receding,” Obama said. “As we look beyond the wars in Iraq and Afghanistan — and the end of long-term nation-building with large military footprints — we’ll be able to ensure our security with smaller conventional ground forces.”

The Obama administration has said it plans to cut $487 billion from the defense budget over the next decade. But the president, Defense Secretary Leon Panetta and other officials didn’t offer details Thursday of where reductions would be made, other than to say they’d shrink the size of ground forces. The details, they said, would be outlined during next month’s budget session.

The implication of further cuts in the size of ground forces suggests that the Pentgon no longer plans to fight prolonged nation-building conflicts such as in Iraq and Afghanistan. Rather, it will invest in drones, unmanned aircraft, cybersecurity and creating a more agile force.

“We’ll continue to get rid of outdated Cold War-era systems so that we can invest in the capabilities that we need for the future, including intelligence, surveillance and reconnaissance, counterterrorism, countering weapons of mass destruction, and the ability to operate in environments where adversaries try to deny us access,” Obama said.

The United States would focus particularly on the Pacific and the Middle East, Panetta said. In Europe, he said, the U.S. strategy would “evolve.”

“Confronting the threats of the 21st century demands greater flexibility to … shift forces,” Panetta said. “How we defeat the enemy may very well vary across conflicts.”

However, experts noted that they’d heard many of these same arguments from former Defense Secretary Donald H. Rumsfeld during the opening months of the George W. Bush administration in 2001. Then came the Sept. 11 terrorist attacks.

“It is easy to emphasize Asia, technology and quality over quantity. In fact, this is what Secretary Rumsfeld did until 9/11 began to force an almost total reversal in every aspect of our strategy and plans less than a year after the Bush administration came to office,” said Anthony Cordesman, a defense expert at the Center for Strategic and International Studies, a nonpartisan research center.

That the Pentagon is discussing cutting Cold War programs suggested that the new budget also could delay the pace of building ballistic-missile submarines, which are designed for conventional warfare, and production of the controversial F-35 Joint Strike Fighter.

The F-35, the most expensive weapons program in U.S. military history, has been riddled with flight and technical problems, raising questions about whether its cost is justified. But the program also has generated jobs in many states, earning it reliable backers in Congress.

The House Democratic Caucus chairman, Rep. John Larson of Connecticut, said Thursday that he was “especially heartened” to hear that the Pentagon wants the F-35 program to succeed.

Critics noted that the Defense Department’s vow to be prepared for any kind of conflict at any time would make it difficult to determine what to cut. Michele Flournoy, the undersecretary of defense for policy, said the department was taking risks by reducing the budget as much as it was, but she didn’t specify what those risks were.

The $487 billion cut over the next decade amounts to roughly 8 percent of the projected budget when adjusted for inflation. But experts noted that the administration will be able to control the budget only for the next five years at most — if Obama wins re-election — and during that period, the budget will drop by only 5 percent in inflation-adjusted dollars over the previous five years.

Assessing spending after that point “is kind of guesswork,” said Lawrence Korb, a defense expert at the left-leaning Center for American Progress.