More than 400,000 acres of wildlands in the Eastern Sierra Nevada should be made protected habitat for an endangered mountain sheep rebounding from the threat of extinction, the federal government said Wednesday.

The U.S. Fish and Wildlife Service's proposed critical habitat designation is a response to a 2005 lawsuit. Environmentalists claim in the suit the Sierra Nevada bighorn sheep couldn't recover because their habitat wasn't protected as required under the Endangered Species Act.

Wednesday's proposal should end the argument, federal officials said.

"The whole purpose of the act isn't just to put species on the list," said Lisa Belenky, an attorney with the San Francisco-based Center for Biological Diversity, which filed the lawsuit. "This is a good first step, because by preserving habitat, you're able to bring the species back from extinction."

The bighorns live much of the year atop the Sierra Nevada's granite peaks, where they forage for sagebrush and grasses. Before the turn of the century, thousands of wild bighorns lived in the high Sierra.

But predatory mountain lions and genetic problems caused by inbreeding have caused the population to crash. Only about 100 were alive as recently as 1998, a year before the Fish and Wildlife Service listed the sheep as endangered.

The proposed 417,577-acre critical habitat area runs from Tuolumne to Tulare counties and juts into the Inyo and Humboldt-Toiyabe national forests, along with neighboring land administered by the Bureau of Land Management.

If the proposal is finalized next year, government agencies and private landowners inside its geographical boundaries will have to consult with the Fish and Wildlife Service to see whether a specific project — like sheep grazing — would jeopardize the bighorn's habitat or its recovery.

Environmentalists say the U.S. Forest Service's decision to allow ranchers to graze domesticated sheep on public lands thought to be crucial to the wild sheep's survival has hurt the bighorn.

The agency is also preparing a draft recovery plan they will use to coordinate wild bighorn recovery efforts with the Forest Service, National Park Service, U.S. Bureau of Land Management and the California Department of Fish and Game, Williams said.

The public can comment on the proposal for the next 60 days, and a final decision is due on July 17, 2008.