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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.