WASHINGTON — One million acres of public land near the Grand Canyon would be off-limits to new uranium mining under an emergency declaration adopted Wednesday by a House committee.

Tapping a rare provision not used in more than 20 years, the House Natural Resources Committee voted 20-2 to stop any new claims to uranium on lands adjacent to the national park for up to three years.

Supporters of the measure, which was advanced by Democrat Raul M. Grijalva of Arizona, said a rush of claims to mine the area for uranium to feed proposed nuclear power plants threatened the natural landscape that lures 5 million visitors to the park each year. The mining, which requires crushing rock and using solvents to remove the radioactive material, could also taint the Colorado River, a drinking water source for millions.

Previous mining near the Grand Canyon has resulted in soil and water contamination that has not been cleaned up, Grijalva said.

"The uniqueness and fragility of the Grand Canyon ecosystem — combined with the legacy of pollution, illness and death left by previous uranium mining — combine to make this the last place on Earth new mining should take place," said Grijalva. "Efforts to belittle those impacts must not be tolerated."

The resolution would have no effect on the more than 10,000 claims already secured on Bureau of Land Management and Forest Service property near the park, according to the Interior Department.

A spokesman for the agency said it would weigh its next steps, given that a 1983 Justice Department opinion found similar resolutions to be unconstitutional.

Republicans, encouraged by Rep. Rob Bishop of Utah, left the room in protest before the vote.

Bishop said the resolution "crossed over the line" and addressed a "supposed emergency that does not exist."

"In essence, I'm leaving this committee," said Bishop. "I will not be part of this process."

Separate legislation pending before the committee, also sponsored by Grijalva, would permanently make the acreage off limits to mining. Environmentalists said the resolution was a good temporary fix.

"This is the best chance for the Grand Canyon," said Christy Goldfuss, a representative of Environment America. "Today, the committee put the Bush administration in a timeout for rubber stamping an assault on the Grand Canyon."

Lawmakers have used an emergency declaration under the Federal Land Policy and Management Act only four other times in history to protect land from energy extraction. The last time was 1983. The committee's vote, which is all that is necessary to temporarily block mining claims, comes as Congress debates more oil and gas exploration on public lands and pushes for the use of more alternative energies, such as nuclear power, which emit less pollution.

The Nuclear Energy Institute in a letter sent to the committee Wednesday accused lawmakers of mischaracterizing uranium mining practices and hampering clean energy development.

"Those practices do not cause cancer or debilitating illness, they are extensively regulated, and they are not a threat to the environment," wrote Alex Flint, the institute's senior vice president for governmental affairs.