Mr. Guinn said the project was based on bad science and public policy, and vowed to block waste storage in his state.

"Let me make one thing crystal clear: Yucca Mountain is not inevitable, and Yucca Mountain is no bargaining chip. And so long as I am governor, it will never become one," the Republican governor said.

"Yucca Mountain is not safe, it is not suitable, and we will expose the Department of Energy's dirty little secrets about Yucca Mountain," Mr. Guinn said.

Congress gave Nevada an unprecedented veto right over the president in its 1982 Nuclear Waste Policy Act, but the act directed Congress to make the final decision.

The 15-year project, which has cost $7 billion to date, will be killed if Congress either upholds Mr. Guinn's veto in a resolution or does nothing.

Once the measure is introduced in the House and Senate, Congress has 90 legislative days to pass or kill it.

House Speaker J. Dennis Hastert, Illinois Republican, has vowed to quickly bring to the floor a resolution to override Mr. Guinn's veto.

A spokesman for Mr. Hastert said Nevada's veto was expected and that a vote on Yucca Mountain in the House could occur as early as May. It is expected to pass the House.

Senate Majority Leader Tom Daschle, South Dakota Democrat, promised Nevadans he would kill the measure, either by not bringing it to the floor or by filibustering it -- a move that would require 60 votes to override.

But under special fast-track rules put into the bill in 1982, any senator can bring up for a vote a measure to override or support Nevada's veto. A simple majority would be required for passage.

"I think the Yucca Mountain issue is dead. As long as we're in the majority, it's dead," Mr. Daschle said in May at a $1,000-per-plate fund-raiser in Las Vegas, 100 miles southeast of the proposed site.

Mr. Daschle backtracked on his threat last month, when he said he learned of the fast-track rule.

"I was not aware that this legislation, when we drafted it decades ago, is under an expedited procedure," Mr. Daschle said.

"Anybody can be majority leader when this comes to the floor," he said.

Instead, Mr. Daschle says it is up to Sen. John Ensign, Nevada Republican, to persuade members of his party to oppose the repository site.

The Energy Department plans to use Yucca Mountain for the disposal of 77,000 tons of high-level radioactive waste and spent fuel being stored at plants throughout the United States.

"It is strongly in the national interest to move forward with the repository, partly with regards to homeland security, energy security and environmental protection," Energy Secretary Spencer Abraham said yesterday.

"Congress should realize the importance in allowing the impartial experts at the Nuclear Regulatory Commission to make a decision on this issue, instead of short-circuiting the process with so much at stake," Mr. Abraham said.

Among the 71 senators who responded to a Congress Daily survey, 36 said they intended to vote in favor of Yucca Mountain, while 14 were opposed and 21 were undecided.

Congress selected Yucca Mountain in 1987 as the only site for consideration. Opponents hope to defeat the proposal by scaring residents of the 43 states through which the waste will be transported.