A federal court has ruled that the Nuclear Regulatory Commission should have held public hearings before it allowed last summer's release of radioactive gas from the damaged reactor at Three Mile Island, and in doing so the court apparently has created another major hurdle for the operators of nuclear power plants.

The Nov. 19 finding by the U.S. Circuit Court of Appeals here "could be very sweeping," said NRC Chairman John F. Ahearne. It appears to require the NRC to hold public hearings for all license alterations other than major emergencies. About 250 proposed changes, mostly minor, are pending before the commission, and public hearings on all of them would bring the NRC machinery to a halt.

"It's a major decision, a major case," Ahearne said. "We're analyzing it now to see what it means."

Radioactive krypton gas accumulated in the Middletown, Pa., reactor after the March 29, 1979, malfunction that spread other kinds of radiation over the surrounding countryside. The krypton kept maintenance crews from entering, and had to be dealt with as the first step in the cleanup.

An NRC staff research report found venting to be the quickest and cheapest approach, with no likely damage to public health. There were protests from citizens' groups and several, including People Against Nuclear Energy (PANEL), filed suit to stop the venting. But the courts declined to intervene and the krypton was vented from June 29 through July 11.

Pane subsequently asked the court to rule on the legality of the NRC's refusal to hold a hearing on its decision. The NRC had found that there were no "significant hazards" likely from the action, and that such a finding meant it did not have to grant a hearing.

The three-judge panel, however, said the NRC had misread the Atomic Energy Act. The law, they said, "only dispenses with requirements of notice and publication" when a no-hazards finging is made, not with the hearing itself.

"The section only permits the NRC to issue a license amendment without a hearing when there has been no hearing request," the ruling said.

Groups opposing nuclear power were delighted with the ruling, and said it would result in more hearings. They denied that frivolous issues might block the permit process.

What's [the NRC's] definintion of a trivial issue?" asked Don Hossler, who filed the suit for PANE. "Nobody here wants to delay the cleanup. But they've called issues of emotional and psychological consequence to people living here as trivial."

Michael Faden, legislative counsel for the Union of Concerned Scientists, said nuclear critics "don't have the time or money to file frivolous requests" for hearings. "But groups will now know they have this right and will take a look at it. The problem has been that an awful lot of serious issues don't get discussed."

The ruling could have a major impact on the NRC's so-called "action plan" -- technical and operational changes ordered for each reactor to fix problems spotlighted by the Three Mile Island accident. Tom Cochran of the National Resources Defense Council noted that the NRC might have to reconsider a controversial ruling that the action plan is not subject to criticism by the public, only to criticism by utility companies -- which presumably will contend that the plan was too stringent.