Sixty-four years ago this week, the Japanese formally surrendered to Allied forces on the USS Missouri, ending World War II. Thus began a long era in U.S.-Japanese relations characterized by a shared strategic vision and broad cooperation on security.

That era may be over. This past weekend's elections ended five decades of dominance by the Liberal Democratic Party. Yukio Hatoyama, leader of the victorious Democratic Party of Japan (DPJ), has questioned some of the most basic assumptions of the U.S.-Japan relationship. While it is too soon to know what direction Mr. Hatoyama's party will take Japan, the Obama administration should not simply sit back and wait for events to unfold.

The new Japanese leader claims he wants a foreign policy more independent of Washington. While Mr. Hatoyama emphasizes that the U.S.-Japanese alliance should "continue to be the cornerstone of Japanese diplomatic policy," he has also said that Japan is "caught" between the U.S. and China. He wants Japan to focus more on Asia and less on America. He has even called for an Asian economic bloc, similar to the European Union, that would use a common regional currency and provide a permanent framework for collective security.

That is not all. Mr. Hatoyama has declared that he would not renew Japan's refueling mission that helps support anti-terrorism operations in Afghanistan and elsewhere. The DPJ also insists that the U.S. Marine Corps air units on Okinawa vacate the island completely. He disagrees with the already negotiated agreement for sharing the costs of redeploying 8,000 U.S. Marines from Okinawa to Guam. And he has even called for reopening the Status of Forces Agreement between the U.S. and Japan.

All of this would be heady change for Japan, a country not known for sudden shifts in policy. For years, the U.S. has prodded Tokyo to take on more global responsibilities for international security and to update the alliance. The DPJ's victory will make achieving these goals even harder.

If the Obama administration sits back and simply reacts to events in Japan, our long-standing alliance may simply wither away. Or worse, Japan may begin to realign itself with other countries such as China in a way that undermines our interests and the security of Asia.

What to do? For starters, the Obama administration should make clear that the United States expects Japan to continue participating in the anti-terrorist refueling operation. How the Japanese handle this issue will be a test of the entire relationship. This operation has never been popular in Japan, so it would be politically easy for the DPJ to jettison it as way to satisfy its constituency and to demonstrate distance from the U.S. The Obama administration should signal that abandoning Japan's obligations on this front will have a political cost internationally.

A second test will be whether the new Japanese government will reopen the Guam agreement. Mr. Hatoyama may try to reshift the U.S. air base on the island, reduce Japan's financial contribution or even move all the U.S. air units out completely. This would be a setback for U.S. military presence in Asia. It could also have unforeseen political consequences for the U.S.-Japan alliance, feeding anti-American sentiments inside Japan, while producing a stateside backlash that would lead Congress to downgrade America's commitments to Japan.

In addition to pushing back on Guam, the Obama administration should emphasize the importance of missile-defense cooperation with Japan. In the past, Japan has been a stalwart U.S. partner on missile defense owing to its concern over the North Korean threat. Highlighting the importance of continuing this cooperation would strengthen an important tie when other threads in the relationship may be fraying. It's also critically important for America's own missile-defense protection that cooperation with Japan continues and be shown to be successful.

The biggest danger to U.S. interests, however, may not be what the Japanese do, but what the Obama administration does in response to the elections. Mr. Hatoyama has not hidden his preference for reaching out to China. But neither has the Obama administration. While some analysts think there are limits to how far Tokyo might cozy up to Beijing, others fear that, when it comes to China, the Japanese are pushing on an open door in Washington. Things like the U.S.-Japan-China dialogue proposed by the administration may suddenly become much more relevant.

It's fine for us to talk with China, but we should not be inserting Beijing in the middle of our alliances. To do so only increases the chances of Japan embracing a strategic realignment that brings it closer to China. Instead of opening a U.S.-China-Japan dialogue, we should continue to build on the existing three-way dialogue -- the one with Japan and Australia -- with the aim of adding more like-minded countries from the region.

That way we can keep our strategic relations with Japan strong -- and see the alliance with the Japanese continue as the true cornerstone of a peace in Asia that began on that day long ago on the USS Missouri.

Kim Holmes is vice president of foreign- and defense-policy studies at the Heritage Foundation.