TOKYO — President Barack Obama, facing withering criticism for a prolonged decision-making process on Afghanistan, asserted Friday he doesn't want the next move to be seen as an "open-ended commitment."

In a joint news conference with Japanese Prime Minister Yukio Hatoyama, Obama also said he was bent on "getting this right." He denied that his administration has been dithering and said that whatever policy change he announces must be aimed at protecting America from terrorist networks.

Opening a weeklong trip to Asia, Obama said the United States and Japan must "find ways to renew and refresh the alliance for the 21st century."

Hatoyama said the two leaders had agreed to spend the next year refining the nearly 50-year-old treaty that defines relations between the two World War II adversaries.

"Both Yukio and I were elected on the promise of change," Obama said. "But there should be no doubt that as we lead our nations in a new direction, our alliance will endure and our efforts will be focused so that it will be even stronger in meeting the challenges of the 21st century."

With Obama weighing a new strategy for Afghanistan, Hatoyama said Japan would end a refueling mission for the U.S. military. But he promised $5 billion in aid for Afghan civilian needs such as schools, agriculture and police.

The new Japanese leader also vowed to cooperate with the United States on combatting climate change and nuclear proliferation.

The trip came as the Obama administration was preparing to announce later Friday that the alleged mastermind of the Sept. 11 terrorist attacks, Khalid Sheikh Mohammed, would be moved from the Guantanamo Bay, Cuba, prison to New York for a civilian trial. Without confirming the details, Obama said Mohammed "will be subject to the most exacting demands of justice."

On Afghanistan, Obama said he was not waiting for any new information. Rather, he said, he wants to be sure he strikes the right balance before committing more U.S. troops and billions of dollars to the 8-year-old conflict.

On a stop at Elmendorf Air Force Base in Alaska on his way to Asia, Obama told a military audience he will commit more forces to Afghanistan only if it is vital to U.S. interests and receives public support.

"I will not risk your lives unless it is necessary to America's vital interests," Obama told the troops.

"And if it is necessary," he said, "the United States of America will have your back. We'll give you the strategy and the clear mission you deserve. We'll give you the equipment and support you need to get the job done. And that includes public support back home."