Using the nation's largest and leakiest nuclear waste dump as a backdrop, Sen. Maria Cantwell (D-Wash.) complained last week that the Bush administration is using a "sneaky" legislative maneuver to avoid cleaning up Cold War-era poisons that are tainting groundwater here and oozing into the Columbia River.

"They are trying to create a loophole in the definition of nuclear waste big enough to drive a truck through and leave Washington state to deal with a mess that we don't want," Cantwell said, echoing the worries of state environmental officials who help monitor the federal Hanford Nuclear Reservation here.

Cantwell's complaint will animate a debate expected this week on the Senate floor. She and Sen. Ernest F. Hollings (D-S.C.) plan to lead an effort to strip language out of the defense authorization bill that would allow the Energy Department to leave some radioactive waste in buried tanks -- rather than get it up and ship it off for entombment in Nevada.

The fight over nuclear waste, which involves Washington, Idaho and South Carolina, has slowed debate on the nearly $450 billion annual defense bill, which pays for everything from the Iraq war to multibillion-dollar weapons systems.

A vote on the Cantwell-Hollings amendment could be close, with Democrats lining up solidly against the Bush administration. Cantwell and her supporters say they are courting several moderate Republicans who often vote against the administration on environmental issues.

The Energy Department maintains that it could save more than $85 billion -- while avoiding the risk of deaths and injuries to cleanup workers -- if allowed to leave the last remnants of nuclear waste in underground tanks and seal it in place with a special kind of concrete.

It is "nuts" to classify all the waste from nuclear bomb production throughout the Cold War as "high level," when a small fraction of it can be safely stored in existing tanks, said Kyle McSlarrow, deputy secretary of energy.

"We want to do this -- not to them, but with them," said McSlarrow, referring to the three states with major cleanup projects underway at old bomb-making sites.

There is considerable disagreement about how dangerous the last remnants of waste are. Cantwell and such groups as the Natural Resource Defense Council point to studies showing that up to half the radioactivity in an underground tank can be contained in the sludge residue at the bottom of the tank.

A federal court in Idaho last year ruled against an earlier effort by the Energy Department to keep some waste in the aging tanks rather than moving it to Nevada for burial beneath Yucca Mountain. Because of that ruling, which is under appeal, McSlarrow said his department urgently needs new language in the defense bill, or "we can't spend money" to continue the cleanup. Cantwell has called this "blackmail."

Here along the Columbia River, Hanford is by far the largest of the cleanup sites. Once the primary factory for making weapons-grade plutonium, the site stores about two-thirds of the country's high-level nuclear waste. It is kept in 177 underground tanks, a third of which have been leaking for decades. Hanford is bordered by the Columbia, the largest river in the West.

The leaks have tainted groundwater, creating a slowly expanding 80-square-mile plume of contamination that violates federal water standards. The plume abuts the Columbia and is a risk to the water supply for Richland, where many scientists and bureaucrats employed in the $2 billion-a-year Hanford cleanup now live.

Last month, the Energy Department persuaded Sen. Lindsey O. Graham (R-S.C.) to introduce language into the defense bill that would allow South Carolina to entomb in concrete and sand some of the waste left over from bomb-building operations at the Savannah River nuclear site near Aiken.

In this, Graham has the support of the governor and state health and environmental officials in his home state. The Energy Department had tried, but failed, to get similar support from state officials in Washington and Idaho.

A key issue is the extent to which the federal government can order states to do its bidding. Graham has insisted that South Carolina will retain final control over cleanup decisions. Most of the waste, he noted, would be shipped to a permanent repository planned for Nevada.

"I would never do this unless my state encouraged me to do it," Graham said. "I wouldn't do this for a second if it was going to jeopardize groundwater."

But his Senate colleague from South Carolina disagrees.

"This is monkeyshines," Hollings said on the Senate floor last month. He warned that the tanks were near a major earthquake fault line and could leak into the Tuscaloosa aquifer or the Savannah River.

What particularly upsets Cantwell about the proposal to reclassify waste is that it was inserted in the defense bill without public hearings and without going through the Senate committee that oversees the Energy Department.

"This is a serious policy change that they are trying to make through closed-door meetings," she said.

Morgan reported from Washington.

Sen. Maria Cantwell (D- Wash.) speaks with Mike Wilson, manager of nuclear waste program for the Washington Department of Ecology.