Obama said he is committed to shutting down networks that plot terrorist activity against the United States, while also avoiding an "open-ended" troop commitment and ensuring that the government of Afghanistan is a reliable partner.

"It's a matter of making certain that when I send young men and women into war, and when I devote billions of dollars of U.S. taxpayer money, that it's making us safer, and that the strategies that are placed not just on the military side but also on the civilian side are coordinated and effective in our primary goal," Obama said.

He said that his decision will be made "soon," and that those who have been critical of the lengthy process "tend not to be folks who, I think, are directly involved in what's happening in Afghanistan. Those who are, recognize the gravity of the situation and recognize the importance of us getting this right," he said.

Obama appeared before reporters with newly elected Japanese prime minister Yukio Hatoyama a few hours after arriving in Tokyo for the start of a weeklong trip to Asia. The trip will span four countries and is Obama's first to the region as president.

During a 90-minute meeting at the Kantei, the Japanese equivalent of the White House, Obama and Hatoyama discussed climate change, Afghanistan, and nuclear proliferation. The leaders exchanged warm praise for each other, embracing the close relationship of their countries. They minimized their differences, such as the location of a Marine Corps airfield on the Japanese island of Okinawa, emphasizing instead their hopes for peace and stability in the region.

Declaring that the United States "is a Pacific nation," Obama said that the futures of the United States and Asia are "inextricably linked" and that his administration "will be deepening our engagement in this part of the world."

During the brief news conference, Obama was queried about Afghanistan, North Korea, and his administration's decision, revealed yesterday, to try Khalid Sheikh Mohammed and other alleged masterminds of the Sept. 11, 2001, attacks in federal court rather than military commissions.

A Japanese reporter asked Obama whether he believed that the United States had done the right thing by dropping nuclear weapons during World War II on Hiroshima and Nagasaki - cities that many Japanese have urged the Nobel Peace Prize-winning president to visit.

Obama did not answer directly. Instead, he expressed his aspirations for a nuclear-free world and said "it would be meaningful for me to visit those two cities in the future." He made a point of noting that Japan was the first stop of his Asian tour - a source of pride here amid growing national anxiety that Japan's importance as a player on the world stage is being eclipsed by the rise of China.

Despite that attentiveness, the Obama administration faces sensitive challenges in its dealings with Japan, including what has become a heated bilateral dispute over the location of the Marine airfield in Okinawa. The dispute is part of a key political commitment - greater Japanese assertiveness in U.S. relations - that helped Hatoyama and his left-of-center Democratic Party of Japan win a landslide election in August.