Energy Secretary John Herrington, acknowledging past lapses, pledged a new "safety ethic" at U.S. nuclear weapons plants Thursday but insisted fast restart of aging federal reactors is "absolutely critical."

In a farewell address at the National Press Club, Herrington said his department has taken long overdue steps to address massive environmental pollution and safety concerns at deteriorating nuclear weapons production facilities, most of which were built in the 1940s and 1950s.Herrington conceded the problems are the result of years of neglect by the government, including inadequate funding for modernization and environmental cleanup and outdated attitudes within his own agency about nuclear safety.

"In the past eight years it has been obvious that the department faced serious challenges," he said. "It was not hard to see that the status of the department's safety and environmental oversight function was not satisfactory.

"Perhaps we have been too lax in this area."

But Herrington maintained at the same time that it is essential for aging reactors to be restarted soon.

"It is absolutely critical that we get our reactors back in operation, and keep them in operation," he said, "until a new generation of reactors comes on line to take their place."

The secretary said his department's renewed safety emphasis is particularly important to ensure reliable restart of the three weapons production reactors at the federal Savannah River Plant near Aiken, S.C.

The three reactors are the sole source of radioactive tritium gas essential for the nation's nuclear weapons program, but they have been shut down for months amid growing safety concerns, including the discovery of cracks in key pipes in the reactor cooling systems.

The Savannah complex's manager, John T. Lowe, said Friday the plant could be restarted immediately if the nation's defense demanded more nuclear weapons material

But Lowe declined to say when he thought the plant in South Carolina nearly 20 miles southeast of here would be restarted.

The shutdown has raised national security concerns because tritium decays rapidly, meaning tritium supplies in warheads must be replenished periodically. Tritium is used to boost the explosive power of war-heads.

Herrington said he believed the SRP problems could be resolved by the spring or summer, allowing restart before a tritium shortage develops. However, he said the current shutdown illustrates the need to be more vigilant on safety.

"Ultimately, the need to meet defense production requirements is linked to the need to meet safety and environmental requirements," he said. "It is not an either-or issue. We cannot meet production requirements 10 years down the road without reliable reactors - and we will not have reliable reactors unless they are also safe reactors.

"This is a major reason why we have moved so aggressively to promote a strong safety ethic," he declared.

Herrington said he welcomed recent criticism by an independent Energy Department advisory panel, which questioned the adequacy of the safety improvement program for the reactors.

In particular, Herrington said the department would carry out the panel's recommendation to conduct ultrasonic testing for cracks in the reactors.

Environmentalists charge the department may not address key safety concerns in the rush to get the weapons reactors operating again. The department wants to resume operation by the summer of 1989 but has acknowledged some equipment repairs at the reactor may take years to complete.