YAKIMA, Wash. (AP) - Gov. Christine Gregoire has implored the federal government to avoid further spending cuts for a waste treatment plant at the Hanford nuclear reservation, saying Washington state would consider legal action or other options if the budget is cut further.

The plant has long been considered the cornerstone of cleanup at the highly contaminated south-central Washington site, which was created in the 1940s as part of the top-secret Manhattan Project to build the atomic bomb. Today, Hanford is the most contaminated nuclear site in the nation, and the waste treatment plant is the government's largest construction project.

However, the project has been mired in delays and cost overruns for years. The U.S. Department of Energy, which manages Hanford cleanup, halted construction on large portions of the plant earlier this year amid seismic concerns and skyrocketing costs.

The Bush administration cited those concerns in its $626 million budget request for the plant for 2006, down from $690 million in previous years. A House-Senate budget committee reduced that amount by another $100 million earlier this month - to $526 million. The Senate approved the spending bill Monday evening.

In addition, the Bush administration has proposed tapping the 2005 budget for $100 million, money that was not spent but was intended to be banked for construction costs in later years. The proposal is part of a $2.3 billion package of cuts across state agencies for hurricane relief.

The budget cuts for Hanford's waste treatment plant clearly violate the federal government's legal obligation to have the plant operating by 2011, Gregoire told a Seattle news conference Monday.

"It is unconscionable, in my opinion, that we are going to delay this yet again. Washington state will not sit idly by while the federal government breaks its commitment to the Pacific Northwest," Gregoire said.

Hanford cleanup is governed under the Tri-Party Agreement, a 1989 legal pact signed by the state, Environmental Protection Agency and the Energy Department. Under that agreement, the plant must be operating by 2011, although that deadline already has been pushed back three times from the original deadline of 1999.

The state will work to fight the latest cuts proposed by the Bush administration and, if unsuccessful, will explore all of its options to fight the federal government, Gregoire said.

State Attorney General Rob McKenna, who joined Gregoire at the news conference, said those options could include a lawsuit or fines.

"Over half a billion dollars still represents a sizable investment and interest in the construction of the waste treatment plant," Energy Department spokesman Mike Waldron said. "The department remains committed to the project, to our cleanup obligations at Hanford and to the goals of the Tri-Party Agreement."

About 53 million gallons of highly radioactive waste, left from decades of plutonium production for the nation's nuclear weapons arsenal, is stewing in 177 aging underground tanks at Hanford. The plant is being built to convert much of that waste into glasslike logs for permanent storage in a nuclear waste repository.

Because some of the underground tanks have leaked into the aquifer, threatening the groundwater and the Columbia River less than 10 miles away, emptying the tanks is a priority.

Once completed, the plant will stand 12 stories tall and be the size of four football fields. It is being designed as it is being built - a method that has proven costly. The price tag already has grown from $4.3 billion to the current $5.8 billion, and construction is only 35 percent complete.

To further complicate the project, a scientific review last year concluded that federal officials had underestimated the impact a severe earthquake could have on the plant.

The Energy Department has since repeatedly refused to release a new cost estimate, although it notified Congress that the cost was expected to rise at least 25 percent. The agency has said a full cost estimate and schedule will not be ready before June 2006.

Washington's congressional delegation expressed support for Gregoire's stand.

U.S. Sen. Patty Murray, D-Wash., criticized the Bush administration for listing the plant as a lower priority program in its proposed cuts for hurricane relief.

Republican Rep. Doc Hastings agreed.

"The governor and attorney general have made clear what actions they're prepared to take on behalf of Washington state, and I stand with them 100 percent," Hastings said in a news release.

"The federal government has a legal and moral obligation to clean up Hanford," Sen. Maria Cantwell, D-Wash., said in a statement late Monday. "Slashing the cleanup budget puts our state at risk and ignores the best interests of all Washingtonians."