Energy Secretary James D. Watkins is moving quickly to tackle the problems of modernizing the nation's problem-plagued nuclear weapons plants and cleaning up their hazardous wastes.

Even before his formal swearing-in Thursday, a team of nuclear experts assembled by Watkins had begun assessing conditions and prospects at key weapons plants to give him an independent view of the problems, department officials said.Members of the Watkins team visited the Savannah River Plant, near Aiken, S.C., last week and were at the Hanford Reservation in Washington state earlier this week, the officials said.

The creation of the team and the start of their work were not announced by the department.

Watkins informed the Senate Energy and Natural Resources Committee late last month that he wanted a special review of efforts at Savannah River to prepare the restart of three reactors there that produce tritium, a perishable and scarce gas needed to make nuclear warheads. The reactors have been shut down since last spring because of safety, technical and management problems.

"This review will provide me with an integrated overview of progress and planned activities" at Savannah River and other key parts of the weapons complex, Watkins said in a written response to questions from members of the Senate panel. A text of Watkins' comments was made available by the panel this week.

The department has said that unless it gets at least one of the Savannah River reactors back in operation by the end of the year, supplies of tritium would be dangerously low.

Will Callicott, a department spokesman, said he could confirm that members of the new review team had visited Savannah River, but he declined to provide more details.

Tom Bauman, s spokesman at the department's Hanford office in Richland, Wash., said two members of the team, Leo Duffy and Fred Carlson, had visited the siteon Monday. He, too, said he could not discuss other details of the visit.

At Watkins' swearing-in ceremony at Energy Department headquarters, President Bush pledged to "waste no time" starting to correct the weapons plants problems, including extensive soil and groundwater contamination at some sites.

"This task is critical," Bush told an audience of several hundred Energy Department employees.

"These problems developed over time and they'll be fully solved only over time, but we'll waste no time getting started on fixing these problems," Bush said.

The department in the waning days of the Reagan administration issued a preliminary plan for spending $81 billion over the next 21 years to modernize and begin cleaning up the weapons complex. Bush has not explicitly endorsed the plan.

At his swearing-in, Watkins said his main goal was to instill a more responsible attitude in Energy Department workers that would lead to sounder practices in the nuclear field.

"Nuclear power demands no less than the best from all who control it," he said. "This, then, is exactly what I ask of my department: a commitment to excellence."