TOKYO (AP) -- Uncertainty over a Marine base and plans to move thousands of U.S. troops to Guam are straining a post-World War II security alliance Japan and the United States set 50 years ago, but Tokyo's new leader said Tuesday he stands behind the pact.
Prime Minister Naoto Kan said he sees the arrangement as a crucial means of maintaining the balance of power in Asia, where the economic and military rise of China is looming large, and vowed to stand behind it despite recent disputes with Washington.
"Keeping our alliance with the United States contributes to peace in the region," Mr. Kan said in a televised question-and-answer session with other party leaders. "Stability helps the U.S.-Japan relationship, and that between China and Japan and, in turn, China and the United States."
The U.S.-Japan alliance, formalized over violent protests in 1960, provides for the defense of Japan while assuring that the United States has regional bases that serve as a significant deterrent to hostilities over the Korean peninsula or Taiwan.
Under the pact, promulgated 50 years ago Wednesday, nearly 50,000 American troops are deployed throughout Japan.
The U.S. forces include a key naval base south of Tokyo, where the only permanently forward-deployed aircraft carrier has its home port; Kadena Air Base, which is one of the largest in Asia; and more than 10,000 U.S. Marines on the southern island of Okinawa.
The large U.S. presence over the past five decades has allowed Japan to keep its own defense spending low, to about 1 percent of its GDP, and focus its spending elsewhere -- a factor that helped it rebuild after World War II to become the world's second-largest economy.
"Even though there are some small problems here and there, in the bigger sense the relationship remains strong," said Jun Iio, a professor at the National Graduate Institute for Policy Studies in Tokyo. "Very few people think that it is actually necessary to make major changes in the alliance."
But while the alliance is one of the strongest Washington has anywhere in the world, it has come under intense pressure lately over a plan to make sweeping reforms that would pull back roughly 8,600 Marines from Okinawa to the U.S. Pacific territory of Guam.
The move was conceived in response to opposition on Okinawa to the large U.S. military presence there -- more than half of the U.S. troops in Japan are on Okinawa, which was one of the bloodiest battlefields of World War II.
Though welcomed by many at first, the relocation plan has led to renewed Okinawan protests over the U.S. insistence it cannot be carried out unless a new base is built on Okinawa to replace one that has been set for closing for more than a decade.
A widening rift between Washington and Tokyo over the future of the Futenma Marine Corps Air Station was a major factor in the resignation of Prime Minister Yukio Hatoyama earlier this month. It could well plague Mr. Kan as well.
Mr. Kan has vowed to build a replacement facility on Okinawa, as the United States demanded, but details are undecided. Implementing the agreement would need the support of the local governor, who has expressed opposition to it.
Mr. Kan was scheduled to visit Okinawa on Wednesday for ceremonies marking the end of the 1945 battle there that hastened Japan's surrender.
Recent tension on the Korean peninsula and China's growing military assertiveness have undoubtedly driven home the importance of the U.S. security pact with Japanese leaders.
Before he stepped down, Mr. Hatoyama suggested that the March sinking of a South Korean warship, allegedly by a North Korean torpedo, contributed to his decision keep Futenma on Okinawa -- reversing a campaign pledge to move it off the island.
Tokyo was alarmed in April when a Chinese helicopter came within 300 feet of a Japanese military monitoring vessel in the vicinity of a Chinese naval exercise. That same month, Chinese ships were also spotted in international waters off Okinawa.
Still, the Okinawa problem underscores an increasingly skeptical stance among some Japanese leaders toward the role of the security alliance.
Though the pact was supported strongly by the staunchly pro-U.S. conservative party that ruled Japan for most of the past 60 years, the newly empowered Democratic Party of Japan, which swept to office last year, has taken a more nuanced approach, saying that while close security ties with Washington remain crucial, Japan needs to improve its relations with its Asian neighbors, particularly China.
On Monday, Mr. Kan said he will reassure Obama when they meet at a summit this weekend that Japan-U.S. ties continue to be "the cornerstone" of Japan's diplomacy.
But he added, "I want to view this relationship from a broader point of view," and stressed Japan must not forget the importance of developing its Asian relationships.