In a ruling that could affect the way many federal agencies do business, the U.S. Court of Appeals here said yesterday that the Nuclear Regulatory Commission violated the Sunshine Act when it closed meetings last summer to plan its annual budget request to the Office of Management and Budget.

A three-judge panel ordered the NRC to release full transcripts of two meetings it had closed, but dismissed as too broad a lower court ruling that it open all meetings "similar in nature" to the closed meetings. Instead, future plans to close meetings must be announced in advance and subject to challenge at the District Court level.

The ruling was proclaimed a great victory by Ellen Block, an attorney for Common Cause, the self-styled citizens' lobby.

"We think this is a significant opinion because it establishes the principle of openness in government," Block said. The ruling, she said, closed "what could have been a significant loophole in the act."

Leonard Bickwit, NRC general counsel, said, "Further appeal is certainly among the options the commission is considering." The Justice Department, as the NRC's lawyer, could appeal either to the full appeals court or the U.S. Supreme Court.

Common Cause representatives sought to attend an NRC budget-planning meeting, were barred and then sued, citing the Government in the Sunshine Act of 1976. That act requires that all meetings of multi-member government bodies be open.

Some exemptions are permitted by the act, but the Court of Appeals held that the exemptions claimed by the NRC did not apply to the budget-planning process.

The NRC had argued that a Sunshine Act exemption permitted meetings to be closed to prevent "premature disclosure" of information likely to "significantly frustrate implementation of a proposed agency action."

"We conclude that there is no blanket exemption for agency meetings at any stage of the budget preparation process," wrote Circuit Judge J. Skelly Wright. He was joined by Ruth Bader Ginsburg and Malcolm R. Wilkey.

"The commission fears that disclosure of its time-honored strategies of item-shifting, exaggeration, and fall-back positions would give it less leverage in its 'arm's-length' dealings with OMB and the president, who make the final budget decisions within the executive branch," Wright wrote.

The Sunshine Act applies only to multi-member agencies, many of them regulatory bodies, and does not affect Cabinet departments headed by a single secretary.

Senior officials in Cabinet agencies are thus free to continue the kind of closed-door wheeling and dealing that inevitably accompanies the budgeting process.