Seven environmental groups, including the National Audubon Society, Wilderness Society, Sierra Club and the Alaska Wilderness League, have countered the proposal by suing Interior Secretary Gale Norton and seeking a more balanced plan for the area, which geologists believe could contain six billion to 13 billion barrels of oil.

Filed in Juneau, the federal lawsuit also names the Interior Department, the Bureau of Land Management and Henri Bisson, the bureau's Alaska director.

The plan designates study areas for caribou and birds, and protects another 1.5 million acres along the coast and some lakes and rivers.

Much of the northeastern section of the reserve already is open to oil and gas exploration, but under tight restrictions with some areas fenced off.