The Energy Department has suspended handling of all plutonium at its Rocky Flats, Colo., nuclear weapons plant because of security breakdowns.

Rocky Flats, perhaps the most troubled of the 17 Energy Department plants that manufacture the components of nuclear weapons, produces the plutonium triggers that ignite nuclear chain reactions. Its manufacturing operations have been suspended since December because of safety and environmental problems. The latest order applies to all handling and movement of nuclear materials, the department's announcement said.

The announcement gave no details of the security breaches. But Beth Brainard, the DOE spokeswoman at Rocky Flats, partially confirmed reports by environmentalists who monitor the plant that sensitivity levels on metal detectors were set so low that investigators were able to carry plutonium out of the plant in their steel-toed work boots.

Investigators from the department's Albuquerque regional office found "several deficiencies" in an inspection of the plant's "safeguards and security," a phrase that "refers to physically protecting weapon components, special nuclear material and classified documents," the department announced.

"There was a situation where they were able to get something going in, not going out," Brainard said. "The detectors were set to accommodate the shoes" of workers going in and out all day, she said. Henceforth, the detectors will be recalibrated, and the workers will wear different types of footgear, she said.

She said Robert M. Nelson, manager of the department's Rocky Flats office, had ordered that "two guards be present and a separate security plan be devised for any materials movement" until the overall security regime is revised.

Energy Secretary James D. Watkins, aiming to restart plutonium processing at Rocky Flats this summer, has ordered a six-week "operational readiness review" that began this week. Brainard said another security inspection will be part of that review.

But the incident has reinforced criticism from environmentalists who oppose restarting Rocky Flats. They said a May 10 memo from Nelson complaining about excessive security procedures and saying he was "unwilling to put significant additional resources toward security improvements" before restart showed that the Energy Department is still putting a higher priority on weapon production than on safety.

"This tells us they aren't exactly ready to restart operations," said Melinda Kassen, a lawyer with the Environmental Defense Fund. "They're out of control at that plant."