Referring to the May timeframe to decide on the base issue, which the United States wants settled at the earliest on the basis of a 2006 agreement, Pentagon press secretary Geoff Morrell said: "It is not the preferred timeline, as far as we are concerned. We've got a lot of work to do and not a lot of time," the Kyodo news service reported.
The base question has become an issue between the two countries since Prime Minister Yukio Hatoyama's Democratic Party of Japan came to power in September, supported by the Social Democratic Party and the People's New Party.
The Hatoyama government wants the Marine base, which includes an air station, moved completely out of Okinawa or even out of Japan. The United States has said there can be no change in the 2006 deal, reached after years of negotiations, calling for relocating the air station to a less populated region on Okinawa and moving about 8,000 Marines to Guam.
Morrell urged Japan to reach a ''positive conclusion'' on the issue ''as soon as possible," Kyodo reported.
The report said Wallace Gregson, assistant U.S. secretary of defense for Asia and the Pacific, separately told visiting Japanese opposition Liberal Democratic Party lawmaker Shigeru Ishiba a longer wait would only make the issue harder to resolve, the report said.
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