The regulatory panel set up by Congress in 1988 to monitor the Energy Department's nuclear weapons manufacturing plants is a federal agency subject to the Freedom of Information Act and other open-government laws, a federal appeals court has ruled.

In a victory for environmental groups, the court said that the Defense Nuclear Facilities Safety Board, which has subpoena power and the authority to impose reporting requirements on the Department of Energy, must function in public like any other regulatory agency.

Judge A. Raymond Randolph, writing for a unanimous panel of the U.S. Court of Appeals here, said that "as a practical matter, we can perceive no reason why Congress would have wanted to shield the board from the operation of FOIA and of the Sunshine Act. . . . Congress may of course exclude the board from FOIA or the Sunshine Act or both. But it has not yet done so and the board must be considered an 'agency' within the meaning of both statutes."

The other members of the panel were Judges James Buckley and Douglas H. Ginsburg.

They brushed aside the arguments given by the regulatory board to justify its practice of meeting in secret: that much of the material it considers is classified and that the law setting it up requires its recommendations to be sent to the secretary of energy before they are made public.

Those arguments are irrelevant, the three judges said, because the only issue is whether the nuclear panel is an "agency" as defined by federal law. It is, they said.

Creation of the Defense Nuclear Facilities Safety Board was part of an attempt by Congress to exert some control over the vast, troubled network of factories and nuclear processing plants that produce and assemble the nation's nuclear arsenal. The factories have been plagued by violations of environmental and safety laws.

Lawyers for the Natural Resources Defense Council and the Energy Research Foundation, persistent critics of the weapons complex, sued last winter to force the Safety Board to open its meetings. They lost in U.S. District Court, but won last week in the appeals court.

NRDC lawyer Dan W. Reicher said that ruling would "compel the board to act in the way Congress intends and the public demands. Allowing the board to function in secret would have bred additional public distrust and thus fundamentally undermined the board's ability to protect the health and safety of the milions of Americans living in the shadow of the bomb plants."

Safety Board Chairman John Conway said the board "will, of course, follow the law." But he said he would have to consult Justice Department lawyers about how to proceed because he said he could not see a way to comply with the law setting up his panel and the Sunshine in Government Act at the same time.