The United States plans to ask Japan to start work in January to make space at Camp Schwab in Nago, Okinawa Prefecture, for relocating the U.S. Marine Corps' Futenma Air Station from Ginowan, a source well versed in the bilateral relationship said Tuesday.

Camp Schwab's barracks will have to be moved to make room for a new airfield that will be used by the air elements now stationed at Futenma, the source said.

As part of an agreement struck in May on realigning the U.S. military presence in Japan, Tokyo and Washington have worked out the plan to build a new airfield with a V-shaped runway using some land at Camp Schwab and new landfill along its coastline.

The forthcoming U.S. request is apparently aimed at making the relocation a fait accompli by getting the work going as soon as possible.

An earlier bilateral accord to relocate Futenma to another part of Okinawa had stalled for a decade partly because protesters blocked the planned construction of an airfield on reclaimed land off the coast.

The Defense Agency plans to build the airfield at Camp Schwab by 2014, taking about three years to conduct environmental assessments and five years for the actual construction work.

Some areas within the U.S. camp, however, are not subject to environmental assessment, and work to demolish barracks there can be started in advance, a senior agency official said.

But another agency official said the envisaged U.S. request could upset the central government's ongoing efforts to win local understanding for the relocation.