Energy Secretary Spencer Abraham acknowledged on Thursday that a proposed Nevada waste dump will be too small to accommodate all the nation's nuclear waste and might have to be expanded.

Under intense questioning from Nevada's two senators, Abraham conceded that the Yucca Mountain repository as currently envisioned could handle only a fraction of the waste expected to be generated by commercial power plants and the government in the coming decade.

Thousands of tons of "this stuff is still going to be (stored) around the country," Sen. John Ensign, R-Nev., told Abraham, who acknowledged that probably would be the case.

The Bush administration has argued repeatedly that the proposed Nevada repository should be built so that radioactive waste now at commercial power reactors and federal sites in 39 states can be consolidated and better protected at a single location.

About 45,000 tons of radioactive waste currently are kept around the country. Another 20,000 tons are expected to be generated by power reactors before Yucca Mountain can be opened, Abraham said.

If a federal license is obtained, the Yucca facility would be scheduled to accept its first waste shipments in 2010. Abraham said it would receive a minimum 3,000 tons of waste a year for 23 years. The industry has estimated that reactors produce about 2,000 tons of new waste annually.

Ensign and his Nevada colleague, Democratic Sen. Harry Reid, said those figures debunk the administration's national security argument, since thousands of tons of waste will remain without a central repository even after Yucca Mountain becomes filled to capacity.

Still, insisted Abraham, any waste taken to Yucca Mountain would be waste no longer kept in less-safe temporary facilities including some near highly populated or environmentally sensitive areas.

After the hearing, Abraham opened the possibility that the Yucca Mountain facility eventually might be expanded. Congress has limited its initial design to 77,000 tons of waste, but Abraham said a future energy secretary after 2007 can consider expansion.

Abraham said the Nevada site has room for more than the initial 77,000 tons. It was unclear how such a move would affect the project's licensing or the likelihood of further legal challenges by Nevada.

President Bush designated the Nevada site as the country's central nuclear waste repository and said he would seek a federal license for it. As was its right under a 1982 nuclear waste law, Nevada filed a formal objection. That can be overridden only by majority vote of both chambers of Congress.

The House already has overridden the Nevada veto. The Senate must vote before July 26, or the Nevada objection will stand. The Nevadans are waging a difficult fight. A survey in this week's National Journal magazine showed that 48 senators already planned to vote against Nevada, with 32 undecided.

Abraham reiterated his conviction that the Yucca Mountain site, which has been studied for two decades, is geologically safe to hold the waste, which will remain highly radioactive for thousands of years.

Nevada's senators have long argued that even if Yucca Mountain were built, thousands of tons of used reactor fuel would still be kept at reactors around the country. They also have argued shipping wastes through 43 states would pose greater risks than leaving the caches where they are.

Abraham rejected the claims that the waste would pose a transportation hazard. The government and nuclear industry has had "30 years of safe shipment of spent nuclear fuel ... without any harmful radiation release," said Abraham.