Filed at 5:36 a.m. ET

NEW ELLENTON, S.C. (AP) -- State troopers got a taste of what might be in store next month during a mock exercise in which they practiced blocking a shipment of plutonium from Colorado.

Gov. Jim Hodges, who is locked in a dispute with the Department of Energy over the shipments, ordered the practice drill Monday for about three dozen state troopers and transport police officers.

As part of the drill, patrol cars blocked a four-lane road near the Savannah River Site, a nuclear facility about 10 miles from the Georgia state line.

Officers declared the exercise a success after managing to convince the driver of an 18-wheel tractor-trailer -- in reality, a vehicle borrowed from the state Department of Correction -- to turn around.

Officials said they didn't know whether it would be that easy when trucks carrying plutonium and escorted by armed federal officers make the same attempted entrance. Energy officials have said shipments could begin by May 15.

``I think they'll turn around,'' Hodges said. But, he added, ``We'll take whatever steps are necessary to keep the plutonium out of here.''

The Energy Department plans to reprocess the plutonium into fuel to be used in commercial nuclear reactors. Hodges worries that the material might be stored in South Carolina permanently.

``The department is extremely disappointed with Governor Hodges roadblock exercise,'' according to a prepared statement faxed by the agency. ``Fortunately other South Carolina leaders are spending their time today working with the department toward finalizing our plutonium disposition program.''

A law professor said the state is likely to lose a standoff with the Energy Department.

The actions of the federal government almost always take priority unless a court gets involved, said Eldon Wedlock, a constitutional law professor at the University of South Carolina School of Law.

``The Supremacy Clause of the U.S. Constitution establishes that the Constitution and the laws of the United States are the supreme law of the land,'' said Wedlock.

Hodges, a Democrat who is up for re-election this year, has threatened to lie down in the road if necessary to block the shipments unless the Energy Department signs an agreement for the treatment and removal of the radioactive materials.

The governor said state officials will have a good idea of when the plutonium will leave the Rocky Flats facility in Colorado and what route it will take.

That will make it a little easier to guess which one of the 69 roads will be used to enter South Carolina, Public Safety Department spokesman Boykin Rose said. He refused to say Monday whether Georgia officials are offering any assistance to keep the material out of the state.