On the way to Tokyo last week, where he began the tour, Obama stopped for a rally at Elmendorf Air Force Base in Alaska.

On Thursday, after a meeting and a brief news conference with South Korean President Lee Myung-bak in Seoul before Air Force One departed, the president visited Osan Air Base. About 1,500 U.S. service members, mostly from the Army and Air Force, gathered under a welcome banner and an American flag to see their commander in chief.

The rally capped a tightly scheduled trip that yielded few concrete accomplishments for Obama. No global warming deal to take to a climate conference in Copenhagen next month. No resolution of a U.S. base dispute with Japan. No movement on a U.S.-South Korea free trade package. No progress with China on disputes over its currency valuation or human rights abuses.

Obama and his advisers are calling the trip a success anyway, because of their higher-altitude goals: showing respect for a region that the U.S. largely ignored after Sept. 11 and reframing the American relationship with China - the world's most populous and most-polluting nation and its third-largest economy - as more of a global partnership.

Neither the U.S. nor China spoke publicly of a "G-2" alliance, but the range of issues covered in talks between Obama and Chinese President Hu Jintao reflected their combined potential to alleviate or aggravate some of the world's biggest problems.

Over the course of Obama's Asia meetings, however, as he sped from Japan to the Asia-Pacific summit in Singapore, to China, to South Korea, the president also had Afghanistan on his mind.

He thanked South Korea and other Asian nations that have made new commitments to the Afghanistan effort, and dealt with concerns about the corruption in Afghan President Hamid Karzai's government and questions about whether any U.S. mission could yield long-term success.

In interviews with U.S. TV networks while he was in China, the president vented his frustration over internal leaks on troop-level discussions, saying he considered that a firing offense.

He's bracing for more questions from European allies next month when he accepts the Nobel Peace Prize in Oslo and global delegates gather for climate talks in Copenhagen.

At Osan on Thursday, the president thanked U.S. troops for volunteering for service in wartime. "Many of you served in Iraq ... others among you served in Afghanistan," he said. "Others among you will deploy yet again."

Many of them await the president's Afghanistan decision with interest. In interviews, some were enthusiastic, others stoic. All said they'd support Obama's decision no matter what. The prevailing expectation was that when his announcement comes, it will be for a sizable troop increase.

Maj. Brad Johnson, 35, of Colorado Springs, Colo., who served in Afghanistan in 2001 and 2002, said the factors going into Obama's decision were "certainly above the levels of what most of us see."

"We all realize a lot more needs to be done there. Can we just up and leave there? Personally, I don't think so. That would be the furthest from what I'd expect."

Air Force Tech. Sgt. Warren Maxson, 41, of Scranton, Pa., who's served in Iraq twice since 2003, said of Afghanistan, "Most people believe that's the more just cause" of the two wars. As for strategy, he said, "We don't talk about win or lose. We talk about what we're supposed to do. Politics ain't our business."

In this part of the world, North Korea remains the more imminent threat, and the president's remarks reflected that. "America's commitment to the defense of the Republic of Korea will never waver, and our alliance has never been stronger," he said.

Earlier in Seoul with Lee, Obama said that U.S. special envoy Stephen Bosworth would travel to North Korea on Dec. 8. That will mark the administration's first bilateral talks with Pyongyang, seen as a precursor to resuming six-party talks on North Korea's nuclear weapons program with China, Japan, Russia and South Korea.