By ANNE GEARAN, AP National Security Writer

WASHINGTON – President Barack Obama wanted to tell a hesitant America why he launched a military assault in Libya, and he wanted to describe it on his terms — limited, sensible, moral and backed by international partners with the shared goal of protecting Libyans from a ruthless despot.

Trouble is, the war he described Monday doesn't quite match the fight the United States is in.

It also doesn't line up with the conflict Obama himself had seemed to presage, when he expressly called for Moammar Gadhafi's overthrow or resignation. Obama's stated goals stop well short of that. And although Obama talked of the risks of a long war, he did not say just when or on what terms the United States would leave Libya.

Obama never directly mention the Libyan rebels seeking Gadhafi's overthrow, even though the heavy U.S.-led firepower trained on Gadhafi's forces has allowed those rebels to regain momentum and push toward Gadhafi's territory.

"We have intervened to stop a massacre," Obama said.

Ten days into a conflict many Americans say they do not understand, Obama laid out a moral imperative for intervening against a murderous tyrant, and doing so without the lengthy international dithering that allowed so much blood to be spilled in Bosnia. His address at the National Defense University echoed campaign rhetoric about restoring U.S. moral pride of place after squandering it in Iraq.

"Mindful of the risks and costs of military action, we are naturally reluctant to use force to solve the world's many challenges," Obama said. "But when our interests and values are at stake, we have a responsibility to act."

Gadhafi's forces have been largely pinned down and unable to mount a massacre since the first hours of the war, while U.S. and NATO warplanes have become an unacknowledged aerial arm of the rebels. Obama said the United States will help the opposition, an oblique reference to the rebels.

Over the weekend U.S. Air Force A-10 Thunderbolt aircraft, designed to provide battlefield support to friendly ground forces, flew attack missions for the first time in this conflict. The Pentagon also disclosed Monday that Air Force AC-130 gunships, low-flying aircraft armed with a 105mm howitzer and a 40mm cannon, had joined the battle. Those two types of aircraft give the U.S. more ability to confront pro-Gadhafi forces in urban areas with less risk of civilian casualties.

The Pentagon's lead spokesman on Libya operations, Navy Vice Adm. William Gortney, told reporters Monday that the U.S. military is not coordinating with the rebels. But he left little doubt that, by design or not, Western air power is propelling the rebels forward.

"Clearly they're achieving a benefit from the actions that we're taking," Gortney said. He displayed a chart that showed rebels advancing within 80 miles of Sirte, Gadhafi's home town.

If the purpose of the U.N.-sanctioned military action is to protect civilians, does that include pro-Gadhafi civilians who are likely to be endangered in places like Sirte that are in the rebels' crosshairs? If not, it is difficult to see the Western intervention as a neutral humanitarian act not aligned with the rebels.

The first goal of the intervention was to prevent a massacre of civilians in Benghazi, the eastern Libyan city where Gadhafi forces were threatening to crush the rebellion two weeks ago. Gadhafi said he would "show no mercy."

A U.S.-led assault quickly accomplished that first goal. A no-fly zone was established two weekends ago with little resistance. The U.S. and its partners then launched airstrikes on Gadhafi supply lines and other military targets not only near Benghazi but around other contested areas as well.

But the role of Western air power then went beyond that initial humanitarian aim, to in effect provide air cover for the rebels while pounding Gadhafi forces in a bid to break their will or capacity to fight.

Now U.S. forces are pulling back, handing much of the responsibility for the open-ended military campaign to allies, as Obama said they would.

"So for those who doubted our capacity to carry out this operation, I want to be clear: The United States of America has done what we said we would do," Obama said with clear satisfaction.

He meant that the U.S. had hewed to its stated role under a U.N. Security Council resolution that authorized force.

But he acknowledged that the U.N. mandate doesn't extend to Gadhafi's ouster, even if many of the nations carrying it out might wish for that. Obama was frank about the reasons why.

"Broadening our military mission to include regime change would be a mistake," Obama said.

It would shatter the international partnership he relies on for diplomatic cover and security backup. It would probably mean sending U.S. ground forces into yet another Muslim nation, something Obama has said he will not do in Libya. It would undoubtedly increase the risk to the U.S. military, the costs of the war and U.S. responsibility for shoring up and protecting whatever Libya might emerge, Obama said.

"To be blunt, we went down that road in Iraq," Obama said, where thousands of U.S. forces remain eight years after the fall of Saddam Hussein.

"That is not something we can afford to repeat in Libya," Obama said.

Getting rid of Gadhafi "may not happen overnight," Obama warned, in his first acknowledgement of the stalemate with the rebels that many analysts and some of his own military advisers suspect is coming. Gadhafi, Obama said, might well cling to power for some time.

The United States is considering arming the rebels, directly or indirectly, and U.S. officials say the U.N. resolution would allow that. Obama mentioned nothing about the possibility of civil war in Libya, or what the U.S. might do if the war grinds on for months.

Obama still faces questions about why Libya and not Yemen, or not Syria. One of his closest national security advisers, Denis McDonough, told reporters Monday that the administration doesn't "get very hung up on this question of precedent."

"We don't make decisions about questions like intervention based on consistency or precedent," McDonough said.

Throughout his address, Obama seemed to be answering his own criticism of past wars and past leaders who committed military force too hastily or too hesitantly.

The Nobel Peace Prize winner never used the word "war" to describe what's happening in Libya, but made a point of addressing what the conflict he chose "says about the use of America's military power, and America's broader leadership in the world, under my presidency."

His book "The Audacity of Hope" and his Nobel speech established the same predicates for U.S. military intervention — an allied coalition and use of multinational power.

"We know that the United States, as the world's most powerful nation, will often be called upon to help," Obama said Monday. "In such cases, we should not be afraid to act, but the burden of action should not be America's alone."

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EDITOR'S NOTE — Anne Gearan has covered national politics and national security in Washington since 1999.