Opponents said his decision, coming less than 24 hours after the step was recommended by the Energy Department, represented a rush into a project that could have consequences for hundreds of thousands of years.

The repository, including details of the packaging and the layout of storage tunnels, has not been designed yet, and many scientific and engineering studies are still under way. The designation starts a clock that will require the Energy Department to apply for a construction license by the end of the year, but the department probably will not be ready.

First, though, the president's action puts the issue before Congress under a system set up in 1982 after what had already been a 20-year search.

What was seen in 1982 as a 16-year plan for finding a location and opening a repository is entering its 20th year and seems likely to last for at least 10 more.

If the Yucca proposal, which is still largely undefined, survives Congress, it will move to the courts, where Nevada has two separate challenges under way already, and to the Nuclear Regulatory Commission, which will have to decide whether to issue a license to let the Energy Department build the repository and, later, bury waste there.

Opponents are seeking to focus the debate on transportation and are predicting that the amount of waste to be moved will fill nearly 100,000 trucks.

Trying to defuse that emerging argument, Energy Secretary Spencer Abraham said in a telephone conference call with reporters today that despite the risk of terrorism, moving the material to Yucca was "safe in comparison to leaving this waste where it is."

The waste is at power plants and weapons factories scattered around the country, including some places that are no longer active industrial plants. Putting it on the road or rails briefly is better than leaving it as a sitting target, Mr. Abraham said. And he pointed out that several utilities were trying to rent space on an Indian reservation near Salt Lake for what he called a "makeshift" storage area, which would also involve transportation.

But approval of Yucca Mountain as the site for the waste is far from certain, and the Energy Department, Mr. Abraham acknowledged, is months at least from being ready to apply for an operating license from the Nuclear Regulatory Commission, as outlined in the Nuclear Waste Policy Act of 1982.

Under that law, the presidential designation first puts the ball in Nevada's court, but the Nevada governor, Kenny Guinn, immediately issued a statement saying he would object.

"I am outraged," Mr. Guinn said, "as are the citizens of Nevada, that this decision would go forward with so many unanswered questions."

The state immediately filed suit in United States District Court here.

Senator John Ensign, Republican of Nevada, said the Energy Department "has been hellbent on shoving waste into our backyard, regardless of what science and common sense show."

The other Nevada senator, Harry Reid, the second-ranking Democrat in the Senate, said Mr. Bush had "betrayed our trust" by not relying on science, as he promised he would in a campaign stop in Nevada.

Nevada has 60 days to object, and then the question goes to Congress.

Yucca Mountain was chosen by Congress in 1987 on a largely bipartisan vote. Lately, however, despite Governor Guinn's position, Yucca Mountain is developing as a partisan issue, with the Democrats seeking to portray it as another assault by the Bush administration on the environment and the Republicans arguing that its selection fills a federal obligation to take the waste, cuts risk and improves energy security, too, by allowing the nuclear industry to keep operating.

Speaker J. Dennis Hastert said, "After two decades of study, we know this remote location beneath the Nevada desert is a safe, secure and viable site."

Mr. Hastert added, "Americans deserve the peace of mind that spent nuclear fuel will be consolidated into one secure location rather than scattered across the country in over 130 various sites."

Some experts took issue with that position.

Arjun Makhijani, the president of the Institute for Energy and Environmental Research, said that moving the waste from the reactors would not cut risk by much if the reactors kept running, as many are now doing under license extensions recently granted by the Nuclear Regulatory Commission.

"It's a shame that the president didn't even take 24 hours on a decision that's the most momentous decision, in terms of time frame, that's ever been made by a president," Mr. Makhijani said.

Representative Richard A. Gephardt, the House Democratic leader, said, "The politics and the needs of corporate energy interests seem to be at the heart of this decision."

Al Gore, the former vice president, said President Bush "did the opposite of what he solemnly pledged to the people of Nevada that he would do" when Mr. Bush was running against Mr. Gore in the presidential campaign.

But John Sununu, the former governor of New Hampshire and the White House chief of staff in the Reagan administration, now lobbying on behalf of the United States Chamber of Commerce, said, "The president made the correct call in recognizing the evidence that supports the designation of Yucca Mountain.