A federal appeals court yesterday tossed out its own judgment supporting a watchdog group's efforts for a wider review of safety issues in the proposed relicensing of the Calvert Cliffs nuclear plant.

Yesterday's ruling, which attorneys and legal experts described as highly unusual, threw more uncertainty into the contentious battle surrounding Calvert Cliffs, the Southern Maryland facility that is seeking to become the first U.S. nuclear plant to gain relicensing.

On Nov. 12, a panel of the U.S. Court of Appeals for the D.C. Circuit ruled 2 to 1 that the NRC's interpretation of rules governing relicensing may have prevented opponents of the plant from having a say in the process. The order filed yesterday vacated the earlier judgment and accompanying majority opinion and directed that a new hearing be scheduled.

However, that cannot occur until another judge is named to replace Judge Patricia Wald on the three-judge panel that heard the Calvert Cliffs case. Wald wrote the now-vacated majority opinion, but she has since departed the court to join the International Criminal Tribunal in the Hague, where she will hear war crimes cases involving the former Yugoslavia.

Critical issues defining the case "were lost in our haste to issue an opinion before our colleague, Judge Wald, departed from the court," Chief Judge Harry Edwards said in a statement accompanying the ruling. "However, in my view, the issues are too important to ignore once uncovered."

Representatives for both sides were stunned at the development.

"Reheard? That's weird," said Stephen Kohn, an attorney for the National Whistleblowers Center, who was out of town when he learned the news yesterday. The nonprofit group is challenging a fast-track process the NRC has established to deal with nuclear plant relicensings.

The news was welcomed at Baltimore Gas and Electric Co., the operator of Calvert Cliffs. "A lot of people will have a happier Thanksgiving," said Karl Neddenien, a spokesman for the utility.

"It reinforces what we've been saying all along, that the NRC process is a thorough process that adequately meets the need for public participation and public involvement," Neddenien added.

Attorneys for the NRC had not seen the ruling yesterday, according to Neil Sheehan, a spokesman for the agency. "In the meantime, we continue to adhere to our position that the commission acted correctly," he said.

The court's ruling hinges on the question of whether changes to the policy governing hearings were made to substantive rules or to procedural rules.

"After considering this matter further, I find that there is good reason to believe that we were mistaken in assuming that the commission acted pursuant to a substantive, as opposed to a procedural, rule," Edwards wrote.

"It's a little mysterious how this escaped the court's attention," said William Kovacic, a law professor at George Washington University who follows the appellate court.

"It is certainly uncommon for a court to reverse itself so quickly," Kovacic added. "But there are cases where they'll do it when it becomes obvious they made a serious mistake."

The NRC would have more legal flexibility in making changes to procedural rules, which are the limits an agency puts on its behavior, Kovacic said.

Kohn said the Whistleblowers will be able to show that the commission's actions were improper and that the question of substantive versus procedural rules "will be a distinction without meaning."