The Energy Department is practicing artificial glasnost -- claiming to be candid about serious problems at the nation's nuclear weapons plants while keeping those problems a secret -- even from Congress.

Energy Secretary James D. Watkins is the one boasting of a new openness, but one of his chief aides, undersecretary John C. Tuck, is being coy with Congress. Tuck has been warding off congressional investigators who are looking for possible safety and security problems.

That's a disturbing sign. For years, the Energy Department operated in a shroud of secrecy, cloaking safety flaws at nuclear weapons plants. The government has finally acknowledged that the safety of thousands of Americans was threatened by accidents and security lapses at the facilities.

It will cost billions to clean them up. Watkins promised an explanation, but he isn't delivering.

Congressional investigators have made numerous requests to review Energy Department files and get copies of documents. But Tuck has stymied those requests and angered some important people. Some in Congress are quietly putting pressure on Watkins to rein in Tuck, and the dispute has raised questions about Watkins's deputies.

Watkins took heat from Congress for nominating Victor Stello to be his assistant secretary with the job of cleaning up the weapons plants. Stello was plagued by accusations that he had covered up problems with nuclear power plants when he was with the Nuclear Regulatory Commission. He finally withdrew his name from consideration for the job.

When Stello bowed out, Tuck got the responsibilities added to his workload until a new assistant secretary is appointed. But politics are his game, not nuclear technology. Some staffers in the department joke that Tuck, "didn't even know what plutonium was until he started the job."

There are signs that Watkins himself hasn't always agreed with Tuck. Sources in the department told us that Watkins has been overheard shouting at Tuck behind closed office doors. A department spokeswoman told us that Watkins is tough on all of his staff. But that isn't evidence enough for congressional staffers that Watkins has his staff under tight control.

Tuck may have offended one too many important people when he crossed Rep. John D. Dingell (D-Mich.) who heads the House committee charged with overseeing the Energy Department. Tuck put road blocks in front of Dingell's investigators.

Dingell is firing back hard. Our associates Scott Sleek and Tim Warner obtained a copy of a letter Dingell recently wrote to Watkins. "I hope you will inform Mr. Tuck that this committee has jurisdiction over DOE and exercises it vigorously," the letter says. "If Mr. Tuck does not wish to cooperate informally, we can arrange more formal, and less pleasant ways."

Dingell does have ways of making Tuck talk. We have learned that the committee has prepared subpoenas for the records, something congressional staffers are rarely forced to do when seeking documents from the Energy Department.

Tuck wouldn't talk to us about the impasse, but department officials said Tuck was doing everything he could to cooperate.