NAHA, Okinawa — A group of Okinawans is suing the Japanese government for allegedly failing to abide by the country’s environmental impact law when it approved a plan to relocate Marine Corps Air Station Futenma to Okinawa’s northeastern shore.

The complainants claim construction of a new airfield on the lower part of Camp Schwab, with runways reaching into Oura Bay, would endanger the threatened Okinawa dugong, a marine mammal related to the manatee.

It was the first such legal action taken in Japan against the plan to replace the Futenma air station in urban Ginowan with a new facility in rural Henoko. The lawsuit was filed Wednesday in Naha District Court.

The suit challenges the Defense Ministry’s April decision to accept an environmental assessment that supported the government’s design for the facility.

"We conducted the necessary evaluation procedures in accordance with Japan’s environmental impact assessment law," said a spokesman for the ministry’s Okinawa Defense Bureau. "We will continue to carry out the procedures appropriately in compliance with applicable environmental impact laws and take the utmost effort to minimize any adverse impact the project would have on the environment."

In April, the ministry said the assessment showed that the facility the U.S. and Japan agreed upon in 2006 met environmental impact standards. It calls for an air facility at the tip of the Henoko Peninsula with part of the V-shaped runways extending into the shallow part of Oura Bay.

The leader of the group of 344 residents and Okinawa conservationists who filed suit said the assessment was a "mere formality" and did not contain the helipads and port facility that are now part of the project.

"The government’s sole intention is to build a military base there, no matter what," said the group’s spokesman, Hiroshi Ashitomi. "Critical information was missing."

He said he hoped that if the Democratic Party of Japan and its allies win control of the government in upcoming elections, they might be more open to listening to opponents of the relocation project.

Construction is scheduled to begin next year and to be completed by 2014. U.S. and Japanese officials have said it is the key to a broader plan to realign U.S. troops in Japan and relieve what has been called the "burden" Okinawa bears for hosting 75 percent of the military facilities used solely by the U.S. in Japan.

Under the realignment plan, some 8,000 Marines and their families are scheduled to move to Guam, and several Marine bases on Okinawa would close.

Opponents of the project, including officials from nearby villages and the prefectural government, have complained that the runways would be too close to Henoko Village and have called for them to be placed farther offshore. Conservationists are opposed to any new construction saying the waters are the feeding grounds for the Okinawa dugong.

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