Washington ? Pending a final environmental review, the Energy Department is expected to move as much as several tons of plutonium and weapons-grade uranium from a federal research laboratory in New Mexico to Nevada because of security concerns, according to documents.

In a department memo, John Browne, director of the Los Alamos National Laboratory, called the proposed move “the best overall decision to meet the post-September 11th challenges for the long-term security of nuclear activities.”

An Energy Department spokesman, Bryan Wilkes, said that while no final decision had been made, moving the material to the Nevada Test Site was the preferred option being studied to increase security. The environmental study was being reviewed, he said.

Several tons of highly enriched uranium and plutonium, which could be used to make an atomic bomb, are kept at Technical Area-18 at the Los Alamos lab in New Mexico where critics have said it cannot be adequately protected.

“There is no doubt that that facility was at high risk. They simply could not defend it,” said Pete Stockton, an analyst for the Project on Government Oversight, a private watchdog group that Sunday released a copy of the Browne memo and other documents involving the expected move.

Built in the 1940s, Technical Area-18 is located at the bottom of a steep canyon, where the high ground and an adjacent highway makes the site difficult to defend.

In repeated security exercises, troops have been unable to protect the material. In a 1997 exercise, Army Special Forces posing as attackers wheeled away a garden cart full of props representing the nuclear material. In another test, attackers obtained access to the facility where they could have detonated an explosion, had they been terrorists.

Had actual material been stolen it would have been enough to make several weapons, said Stockton, who three years ago chaired a DOE team that recommended to then-Energy Secretary Bill Richardson that the material be moved.