A federal appeals court ruled yesterday that the Nuclear Regulatory Commission unfairly ignored opponents of the Calvert Cliffs nuclear plant as it rushed to renew the license for the facility, which generates enough power to supply 450,000 homes.

The 2 to 1 ruling by a panel of the U.S. Court of Appeals for D.C. Circuit represents a rare reversal for the NRC and may have far-reaching implications for the nuclear power industry, which is closely following the case. Calvert Cliffs is the first nuclear plant in the country to seek a 20-year renewal of its license, but five others have started the process and about 20 others have expressed interest.

The NRC, under pressure from the industry and Congress, has established a fast-track process for renewing nuclear licenses, and Calvert Cliffs is viewed as a test case.

"It's going to have a massive impact," said Stephen Kohn, attorney for the National Whistleblowers Center, the group that successfully challenged the new NRC process, claiming that the streamlining comes at the expense of public safety. "It's party time. . . . The commission is getting the message that they can't just change the rules."

The relicensing of Calvert Cliffs in Southern Maryland, which generates about half of Baltimore Gas and Electric Co.'s electricity and is the largest private employer in Calvert County, was to have been approved this spring. But the court's decision could delay the process by three years, Kohn said, citing the NRC's own estimates.

Should the NRC determine that it improperly denied the group a time extension--as the judges in the majority strongly implied it did--"the Commission must allow it an opportunity to meaningfully participate in the remainder of the proceeding," the court said in an opinion written by Judge Patricia M. Wald, who was joined by Chief Judge Harry T. Edwards.

A dissenting opinion by Judge Stephen F. Williams had not been filed as of yesterday.

"We feel the NRC acted properly," said Karl Neddenien, a spokesman for BGE. "We need to take a look at the decision and determine what the course of action will be."

Diane Screnci, a spokeswoman for the NRC, said that "it's too soon to tell" what impact the court's ruling will have on the relicensing process.

"The court has asked us to reevaluate whether we improperly denied the time extension, and certainly we'll do that," Screnci said.

Kohn, however, did not hesitate to assess the ruling's impact.

"What makes this so sweeping is its potential impact on . . . other plants that want relicensing," he said. "It's important because now, citizens groups across the country which want to intervene can do so, and now have strong procedural rules."

The majority opinion noted that "the NRC for the first time . . . adopted a stringent interpretation" of the rules governing involvement by groups seeking to review the safety of the plant.

In August 1998, a licensing board rejected the Whistleblowers' motion for an extension of time for reviewing the plans, stating that the group failed to meet its burden of establishing "unavoidable and extreme circumstances" justifying an extension. The NRC turned down the group's appeal.

"At the very least, it is strongly possible that Whistleblower would have received the extension because it had asserted factors which had been approved by the commission in the past as sufficient to justify good cause for an extension," the court wrote.

Last month, the NRC issued a report recommending relicensing for Calvert Cliffs, declaring that the risks of any adverse environmental impact are too small to justify closing the plant on the shore of the Chesapeake Bay.

The group wants its experts to be given the opportunity to examine the plant for potential safety hazards, inspecting pipes and ventilation systems, for example.

"We need our experts to review their records, and that's exactly what NRC and BGE didn't want," Kohn said. "The public is the absolute biggest winner on this, because now the commission cannot undermine meaningful public participation."

The NRC established a streamlined process in an attempt to remove some of the uncertainty faced by utility officials who want to know whether they will be able to continue to operate nuclear plants after the initial 40-year licenses expire. The operators of many of the country's more than 100 nuclear plants are "without question" watching the Calvert Cliffs case, said Steven Kerekes, of the Nuclear Energy Institute, a lobbying group for the industry.

The licenses for the two reactors at Calvert Cliffs do not expire until 2014 and 2016, but BGE applied for early renewal in order to plan for alternatives in the event the applications are turned down.