The Interior Department on Wednesday opened nearly half a million acres of federal land in an ecologically sensitive area of Alaska's North Slope to oil and gas development.

The department said it would allow oil development in virtually all of the wetlands surrounding Lake Teshekpuk in the northeast corner of the National Petroleum Reserve-Alaska. The lake region includes one of the most important molting areas in the Arctic for wild geese and areas sought out by caribou herds for calving.

The plan calls for opening seven leasing areas, from 45,000 acres to 60,000 acres, north of the lake and other acreage south of the lake to oil and gas development. The government estimates that the areas surrounding Lake Teshekpuk contain about 2 billion barrels of economically recoverable oil and 3.5 trillion cubic feet of natural gas.

Henri Bisson, the Bureau of Land Management's director in Alaska, said the leasing program would include thousands of acres around the lake where no surface facilities — except for pipelines — would be allowed as a way to protect caribou calving areas and geese molting areas.

"We think we have a very (environmentally) responsible proposal here," Bisson said in a telephone interview. He said surface facilities, including roads and drilling pads, would be limited to no more than 300 acres for each leasing area.

Environmentalists called the restrictions inadequate.

"It's not good for the geese and it's not good for the caribou," said Stanley Senner, executive director of the Audubon Society in Alaska. He said the plan enables construction of scattered oil and gas facilities, airstrips and gravel mines in an area that long has been protected from oil development.

In 1923 the government set aside the 22 million-acre National Petroleum Reserve-Alaska for its oil and gas resources. It is located west of the Prudhoe Bay oil fields; the Arctic National Wildlife Refuge, which has been at the center of a drilling dispute in Congress, is east of Prudhoe Bay.

Most of the NPRA was opened to development in the 1990s, but not the 4.6 million-acre northeast section that includes the ecologically sensitive Lake Teshekpuk region. It had been expected that most of the northeast region also was slated for leasing, but environmentalists had hoped to keep oil rigs out of the region around Lake Teshekpuk.

"Apparently 87 percent (of the region) wasn't enough for the oil companies," said Eleanor Huffines, Alaska director for the Wilderness Society. She called the BLM's restrictions on development in the lake area "window dressing" to disguise the fact that drilling will be allowed in what she called one of the North Slope's most important wetland areas.

The BLM concluded a year ago that oil and gas exploration in the northeastern section can be conducted with "minimal impact" on the area's wildlife. The decision Wednesday represents a final go-ahead for such development.