A prolonged delay in restarting nuclear weapons reactors could jeopardize national security, say Pentagon officials who expressed relief at an Energy Department announcement that it planned to resume production of tritium early next year.

"Obviously, the sooner the better as far as we are concerned," a Pentagon official said Wednesday. "Tritium is absolutely essential for the production of warheads" on modern thermonuclear weapons, said the official, speaking on condition that his name not be used."If (the reactors) are not started for several years, then we might begin to have trouble," said the source. Officials at the Defense and Energy Departments said that for security reasons they could not specify the exact amount of tritium that the government has and needs, or when a shortage would become critical.

In a related development, Energy Department spokeswoman Gail Bradshaw said tests showed no health threat to three workers exposed to radiation at a nuclear weapons facility, the Rocky Flats plutonium processing plant in Golden, Colo., on Sept. 29. The plant has been closed by the government for safety reasons.

Energy Secretary John S. Herrington, seeking to defuse criticism of lax safety standards at nuclear facilities, announced Tuesday that one of three tritium-producing reactors at the Energy Department's Savannah River Plant, in Aiken, S.C., will begin "a phased start-up" in December, culminating in January.

The three reactors at Savannah River have been closed down since August for safety and maintenance checks.