Recent revelations about serious safety and security problems at U.S. nuclear weapons production facilities have left the Department of Energy reeling.

Energy Secretary John Herrington felt it necessary last week to call a press conference to say that things aren't as bad as they seem.From there, Herrington and national security adviser Colin Powell briefed President Reagan on the state of the nuclear weapons production system and whether it is still able to perform its mission, about which there are serious doubts.

DOE safety chief Richard Starostecki has likened the situation to the one within the space program before the Challenger accident: an institutionalized mindset that emphasizes meeting production requirements over all other considerations.

For the past six years, there have been a series of congressional reports and probes revealing major problems at individual plants or systemwide. The past year has seen a crescendo of scandals.

What is now known about the nation's 15 nuclear weapons production facilities appears to amount to a problem of monumental proportions: Environmental contamination is widespread, with an estimated cleanup cost of $100 billion over the next 30 years; the cost of modernizing aging plants and bringing them into compliance with safety and health regulations is put at another $100 billion.

There are also the questions of whether DOE, which has fought change every step of the way, is willing to face its problems, and whether Congress and the next administration, under severe budget pressures, will be willing to deal with the problem.

Still, recent events guarantee the issue will continue to receive national attention. Those events include:

- The shutdown of the Denver Rocky Flats plutonium processing plant, Building 771, on Oct. 8. The decision to shut down the building, which reduced activity at Rocky Flats to a crawl, came after a DOE safety inspector and two workers were inadvertently contaminated with radioactive plutonium. Rocky Flats is the only government facility that fabricates plutonium triggers for nuclear warheads.

- A strike by 632 workers at DOE's Feed Materials Production Center in Fernald, Ohio, over wages and safety conditions, which has halted production. The facility is the system's only uranium processing plant.

- All three nuclear reactors at DOE's Savannah River plant near Aiken, S.C., have been shut down since August. DOE officials say they can't restart any until January. The plant is the only U.S. producer of plutonium and tritium for use in nuclear warheads. Tritium decays at a rate of 5.5 percent a year; without a fresh supply of tritium soon - exactly when isn't clear - some weapons may become inoperable.

- A General Accounting Office report released last week found major security lapses at the three major weapons research labs: Los Alamos and Sandia in New Mexico, and Lawrence Livermore in California. Dozens of foreigners - including three suspected of being Soviet-bloc spies - were allowed access without security clearances, the report said.

The root of these and other problems lies in DOE's management practices and those of its predecessor, the Atomic Energy Commission, which for decades cloaked the operation of these facilities in secrecy, according to congressional investigators.

The situation was exacerbated under the Reagan administration, which accelerated nuclear weapons production without modernizing aging facilities or revamping their management.

Still, Weiss said the blame doesn't belong solely to the Reagan administration. "This problem goes back 30 years. Every administration in that time has to share some of the blame for it," he said.

Now even some of DOE's sternest critics believe its top management has come to recognize the seriousness of the problem.

In December DOE is scheduled to deliver to Congress a long-term plan for cleaning up environmental contamination, improving safety and modernizing facilities. The report is expected to become the focal point of debate in the next Congress over how to proceed.

"It's still going to take a lot of external pressure to make the changes come more quickly," Weiss said. "I don't think they will change quickly by themselves."