U.S. District Judge Alan McDonald ruled last month in Yakima that Initiative 297, now called the Cleanup Priority Act, was unconstitutional. The initiative would bar the government from accepting more nuclear waste at the Hanford nuclear reservation until the waste already there has been cleaned up.

Attorneys representing the state Department of Ecology filed a notice of appeal with the 9th U.S. Circuit Court of Appeals in San Francisco on Wednesday.

"We respectfully disagree with the federal district court's conclusion that Initiative 297 is unconstitutional and we are not content to let this decision rest with a single district court judge," McKenna said in a news release from Olympia.

Voters approved I-297 by a nearly 70 percent margin in 2004. The federal government immediately filed suit to overturn it.

Sponsors of the initiative applauded the state's action Wednesday and pledged to work with McKenna and Gov. Chris Gregoire in moving the appeal forward.

"Sponsors of I-297 believe an appeal is vital to protect the state's interests because, if left unchallenged, the lower court ruling places at risk state authority to require the federal Energy Department to empty high-level nuclear waste tanks and to clean up the leaks from those tanks," Heart of America Northwest, one of the sponsors, said in a release.

"USDOE has proposed to abandon 10 percent of the waste in the tanks and has sought to have the state agree to plans that would avoid cleanup of the spreading contamination," the activist group said.

"We believe the district court correctly ruled that I-297 is unconstitutional and that the court's ruling will be upheld on appeal," Energy Department spokeswoman Megan Barnett said in an e-mail from Washington, D.C. "We remain committed to safely cleaning up Hanford under the Tri-Party Agreement."

McDonald ruled that the initiative is unconstitutional because it violates federal authority over nuclear waste, as well as the Constitution's interstate commerce clause.

He also found that the initiative impairs the Tri-Party Agreement, a consent enforcement order signed by Ecology, the U.S. Department of Energy and the U.S. Environmental Protection Agency to govern cleanup at Hanford.

"Given the high level of public interest and the importance of this issue, the state of Washington's perspective needs to be reviewed by the Ninth Circuit," McKenna said.

His office had argued that the state has authority to regulate hazardous wastes, including radioactive materials. The state also argued that the federal government could not strike down a law without first seeing how it would be applied.

Hanford was built in the 1940s as part of the top-secret Manhattan Project to build the atomic bomb. It continued to produce plutonium for the nation's nuclear arsenal for 40 years.

Today, it is the nation's most contaminated nuclear site. Cleanup costs are expected to total as much as $60 billion, with the work to be finished by 2035.

Last July, the Washington state Supreme Court ruled that parts of the initiative could stand even if a federal judge found other parts unconstitutional. McDonald, however, struck the measure down in its entirety.