The bid-rigging scandal involving the Defense Facilities Administration Agency widened Thursday after investigators said bids for a runway relocation project at the U.S. Marine Corps Iwakuni Air Station in Yamaguchi Prefecture were also rigged.

Contractors were found to have won bids by tendering quotes closely matching the cost estimates of the agency, which manages Self-Defense Forces and local U.S. military facilities, the investigative sources said.

The successful bids in most cases came within at least 95 percent of the cost estimates.

The projected bid included those for breakwater construction, land-fill work and foundation improvement projects that began at the base in fiscal 2004, the sources said.

A bid for land-fill work involving the runway, for instance, was awarded to a consortium of general contractors for 2.73 billion yen. The agency's estimate was 2.79 billion yen.

Prosecutors have searched major contractors, including Kajima Corp., Taisei Corp. and Shimizu Corp., and are analyzing materials seized as evidence, the sources said. They also searched Obayashi Corp., Tekken Corp. and Maeda Corp.

To reduce noise and ensure the safety of residents near the base, which is jointly used by the marines and the Maritime Self-Defense Force, the government began a project in 1997 to relocate the air station's 2,440-meter runway 1 km farther offshore.

The whole project is expected to be completed in fiscal 2008 at a cost of 240 billion yen.

As part of realignment plans for U.S. forces in Japan, Washington wants to relocate carrier-based aircraft from the Atsugi Naval Air Facility in Kanagawa Prefecture to the 574-hectare Iwakuni base, which is the only marine air station on Honshu.

The agency's third-highest ranking official, his predecessor and an official at the agency's general affairs department were arrested Monday for allegedly rigging bids on two occasions for air-conditioning systems at a new SDF hospital and a new DFAA building in Tokyo.

The bid for a ventilation project at a U.S. hospital planned to be built in the U.S. Marine Corps Camp Foster in Okinawa was also allegedly rigged by agency officials.

Iwakuni plebiscite

YAMAGUCHI (Kyodo) The city of Iwakuni will hold a nonbinding plebiscite on whether it should accept the transfer of a carrier-based U.S. air wing from Atsugi Naval Air Facility in Kanagawa Prefecture, city sources said Thursday.

Mayor Katsusuke Ihara will announce the decision soon, the sources said. The date of the plebiscite -- the first over the plan to realign U.S. forces in Japan -- has not been set yet. But an Iwakuni ordinance stipulates it must be held within 90 days.

Ihara said he wants the issue settled before the city merges on March 20 with other towns and villages in Yamaguchi Prefecture.

He acknowledged that the city and its assembly differ on the issue.

Some members of the municipal assembly have said they are ready to accept the relocation plan in exchange for concessions on other base-linked problems, but the mayor opposes the plan and has demanded it be scrapped, claiming safety concerns.

The city ordinance allows the mayor to propose a plebiscite, and the mayor and the assembly have said they "will respect its outcome."

Iwakuni has a population of about 107,000 and faces the Seto Inland Sea.

The base is jointly used by the U.S. Marine Corps and the Maritime Self-Defense Force.