Idaho's effort to block the resumption of radioactive waste shipments into the state has been taken before a federal appeals court.

A three-judge panel of the 9th U.S. Circuit of Appeals in San Francisco is expected Tuesday to consider Idaho's request for an emergency stay to block shipments of waste from a decommissioned nuclear power plant in Colorado.Shipments could start the 690-mile trip from Platteville, Colo., to the Idaho National Engineering Laboratory as early as May 20. But the state says that would expose Idaho residents to the threat of radiation.

The state's motion for an emergency stay, backed up by 50 pages of depositions and exhibits, was filed with the 9th Circuit Court on Friday, just hours after the state was notified that the Department of Energy plans to start accepting waste shipments at the laboratory site in southeastern Idaho.

The shipments will be from the decommissioned Fort St. Vrain nuclear power plant operated by Public Service Co. of Colorado. The official notice sent to state and local officials Thursday said there is about 4,000 cubic feet of radioactive waste, which could take nearly 250 truckloads.

The shipments would take place over six to 18 months. Notice of the shipments also was sent to officials in Colorado, Wyoming and Utah, whose roads would be traversed by the shipments.

Gov. Cecil Andrus closed Idaho's borders to additional shipments of nuclear waste in 1988, and they have remained closed since then.

Earlier this month a federal judge ruled the ban was illegal, setting up the state's appeal to the 9th Circuit Court.

Idaho's request for a stay contends the 1982 Nuclear Waste Policy Act has been violated because the Department of Energy, which operates the sprawling laboratory, has not completed an environmental assessment on the risks of the shipments.

State Attorney General Larry EchoHawk said a lot is riding on the state's request for a stay.

"If we lose that effort and the shipments actually take place, it is going to be very difficult to ever send the material back," he said in an interview Friday.