Oregon plans to join the state of Washington's lawsuit against the Department of Energy to force it to complete the cleanup of Hanford, Oregon Gov. Ted Kulongoski and Attorney General John Kroger announced Wednesday.

"Further delay is unacceptable," Kulongoski said in a statement. "The federal government must make this cleanup a priority and meet its obligations to address the environmental and public health risks that the Hanford site continues to pose."

The state of Washington filed a lawsuit in late November in an attempt to force DOE to move faster to empty radioactive waste from underground tanks at the Hanford nuclear reservation and treat the waste. The suit was filed after DOE fell years behind schedules in the legally binding Tri-Party Agreement.

A motion to allow Oregon to enter the lawsuit as an intervenor was expected to be filed late Wednesday or today. The federal government has not indicated whether it will oppose the move, but Washington state officials were pleased.

"We welcome Oregon's support in this necessary litigation," said Washington Gov. Chris Gregoire and Attorney General Rob McKenna in a jointly issued statement.

Both states rely on clean, safe water to support their economies and the health and the well being of their residents, they said. Washington and Oregon counties south of Hanford have 57,000 companies that rely on water to provide 780,000 jobs, they said.

If not cleaned up, Hanford's hazardous waste also puts at risk the traditional fishing grounds of the Confederated Tribes of the Umatilla Indian Reservation, according to Oregon. The Columbia River runs through the nuclear reservation, which was left with contaminated soil and ground water by the past production of plutonium for the nation's nuclear weapons program.

Some of the underground tanks have leaked an estimated 1 million gallons of radioactive waste into the ground in the past, and the states are concerned that the longer the cleanup takes, the more soil could be contaminated.

Washington negotiated for major changes in the cleanup deadlines for 18 months before announcing that the negotiations failed to produce an agreement that the state believed had legal safeguards to ensure that cleanup deadlines were met.

"We had no reasonable alternative but to file our lawsuit in November to seek relief from the U.S. District Court," said the statement from Gregoire and McKenna. "We welcome Oregon's support in this necessary litigation."

Earlier this week Gregoire met in Washington, D.C., with new Energy Secretary Stephen Chu and Attorney General Eric Holder to discuss the lawsuit. Before the lawsuit was filed the state indicated it had reached an agreement in principle on changes to the Tri-Party Agreement with former Energy Secretary Samuel Bodman, but then could not agree with the Department of Justice on the legal language the state believed would ensure the deadlines were enforceable.

Although no further talks have been scheduled, Gregoire said Holder suggested a small team be assembled to negotiate a settlement.

"Our goal as a state is to come out of this whether through a settlement or a decision on the merits in litigation with enforceable commitments to complete Hanford tank retrieval and tank waste remediation," said Andy Fitz, a Washington state assistant attorney general.

The worst of the waste will be treated at the vitrification plant, which is required under the Tri-Party Agreement to begin operating in 2011, but is not expected to be ready until 2019.

Until Hanford has a way to start treating at least some of its 53 million gallons of tank waste, there is limited space in newer double-shell tanks to hold waste emptied from leak-prone single shell tanks. The pumpable liquid already has been removed from single shell tanks, but 30 million gallons of waste remains.