"This administration is committed to ensuring America's national security and the security of the people of South Carolina are maintained by proceeding with a program to dispose of weapons grade plutonium in a safe and responsible manner," said Energy Department spokesman Joe Davis.

Davis said the United States agreed in a September 2000 treaty with Russia that each side would dispose of 34 metric tonnes of weapons-grade plutonium.

He said the June ruling by U.S. District Court cleared the way for shipments to begin to the Savannah River nuclear facility, including some six metric tonnes from the Rocky Flats nuclear facility near Denver, Colorado.

He had no immediate details on how much of the plutonium had already been shipped to the facility since June.

South Carolina Gov. Jim Hodges signed an executive order last week declaring the plutonium a threat and ordering state police to stop any vehicle attempting to carry it into South Carolina, but the court said he could not block the shipments.

Tuesday's ruling upheld that decision, but Hodges, a Democrat seeking re-election in November, vowed to take his battle to the Supreme Court.

'NUCLEAR DUMPING GROUND'

"I spent the last four years trying to end South Carolina's role as the nation's nuclear dumping ground and I don't want us to go back," Hodges said in a statement. At the Savannah River site 160 miles (260 km) southwest of Charlotte, the plutonium is to be converted into fuel for commercial nuclear reactors.

The Department of Energy is under pressure to start shipping it soon because it plans to shut down the Colorado facility by 2006 and must move the plutonium this year to stay on schedule.

South Carolina has never objected to temporarily holding such plutonium. But Hodges questioned the environmental impact and sought legal guarantees that the federal government would follow through on plans to convert the plutonium to reactor fuel, saying he feared the state would become a permanent dumping ground for nuclear waste.

In its ruling on Tuesday, the three-judge appeals court panel said it had reviewed the Energy Department's actions and felt it complied with federal environmental requirements.

"We are satisfied that the DOE took a 'hard look' at the environmental consequences of its proposed course of action," the judges said, noting that the department's decision to store the plutonium there was "neither arbitrary nor capricious."

Davis said the department was proceeding with its plans. The appeals court has confirmed that we've made all the right decisions, and we're moving forward," he said. He had no comment on Hodges' decision to take the case to the Supreme Court.