MISAWA AIR BASE, Japan — Lt. Gen. Bruce Wright is the top U.S. military representative in Japan, Washington's most important Asian ally. He's also a seasoned combat pilot, just back from an afternoon in his F-16 fighter flying maneuvers over the Japan Sea, taking in a tense region from 11,000 feet up.

Not far over the horizon is North Korea with its nuclear ambitions, and rising China, with its vast army and designs on U.S. ally Taiwan. Below him is Japan, where 50,000 U.S. troops maintain the balance of power. Farther off, Islamic troubles simmer in Thailand, Indonesia and the Philippines.

"You just have to take a look around the region to see why it is so important," he said in an interview. "The size of militaries, and in fact the growing military capabilities in this region, certainly gets my attention."

The Washington-Tokyo alliance is critical — and evolving.

With U.S. military resources drained by Iraq and the global war on terrorism, the two countries are in talks that could lead to the most sweeping realignment of U.S. troops in Japan — and the biggest shift in Japan's own leadership role — in recent memory.

Officials on Wednesday said they reached agreements in two important areas to ease friction between Americans and locals on Okinawa, where most of the 14,500 Marines in Japan are stationed. They agreed to move a Marine airfield to a less crowded area of the island and shrink the number of Marines by thousands.

But the aim of the talks runs much deeper than merely logistics.

Washington wants a stronger Japan playing a more vigorous role in regional security issues and, perhaps, serving to counterbalance China's rising strength.

Prime Minister Junichiro Koizumi backs that shift. He has sent hundreds of troops to Iraq in a humanitarian role and supports efforts to revise Japan's post-World War II constitution, which severely restricts the use of its military.

"There is tremendous promise for Japan to be an international security leader," Wright said. "We have proven to the world that Japan and the U.S. can be mutually supportive partners. ... I have a lot of confidence in Japan."

Japan already has 250,000 troops and modern ships and fighter planes. Japanese and U.S. troops also have significantly boosted their ability to work together, from refueling each other's ships and planes to improving command communications.

But many Japanese believe their country should learn the lessons of its World War II aggression and stick to diplomacy, aid and political leadership abroad.

Koizumi's insistence on visiting a shrine in Tokyo closely associated with pre-1945 militarism has raised concerns around Asia as well. His latest visit on Oct. 17 provoked strong protests from South Korea and China.

The talks in Tokyo have an added sense of urgency because the United States is scaling down its forces in South Korea from 37,000 to 24,500.

Okinawa may be headed for similar reductions, after negotiations so protracted that many Japanese read a gesture of impatience in Defense Secretary Donald H. Rumsfeld's decision to skip Tokyo when he toured Asia this month.

Wright acknowledged the talks have been complicated but believes they have shown "a lot of progress."

Washington has good reason to want a strong Japan.

North Korea has one of the world's biggest standing armies and missiles that can reach virtually any of the dozens of U.S. military facilities in Japan, possibly even the American West Coast.

Islamic insurgencies are long-standing in the Philippines and southern Thailand. Al-Qaida has been linked to terrorism in Indonesia. Piracy is a constant threat to shipping in the Strait of Malacca, which connects the Indian and Pacific oceans.

And then there is China, its tensions with Taiwan and its increasingly heated territorial disputes with Japan. China's rising economic and military power is generating concern, although U.S. officials are careful not to call Beijing a threat.

"It's my job to plan for the worst case," Wright said. "I think the best thing to say about China is that we look forward to increased transparency regarding Chinese military growth."