A nuclear safety panel ruled yesterday that the Oyster Creek Nuclear Generating Station in Ocean County can operate safely for the next 20 years, clearing the way for a final decision as soon as next month by the U.S. Nuclear Regulatory Commission on the fate of the nation's oldest nuclear power plant.

Opponents of the plan immediately said they would appeal the ruling.

The Atomic Safety and Licensing Board, based in Rockville, Md., which held public hearings on Oyster Creek last summer, rejected a challenge by six community groups to the relicensing application for the Lacey Township plant.

The groups asked the panel to block the NRC from considering a new license for Oyster Creek, claiming that a plan by plant owner AmerGen Energy Co. LLC to manage corrosion in a drywall region surrounding the reactor is inadequate.

Specifically, the groups say the company's plan to do ultrasonic testing measurements in a sand bed region near the bottom of the vessel every four years is not often enough.

Richard Webster, the attorney for the community groups, said he would file an appeal as soon as possible.

"We are hopeful that in the fullness of time, we will prevail," he said.

Webster said he was heartened by a slight dissent from one of the panel's members, Administrative Judge Anthony Baratta, who wrote that he is not convinced that AmerGen has proved that monitoring every four years is sufficient to ensure safe operation.

Supporters don't want to see the nuclear plant, its electricity and its hundreds of high-paying jobs vanish. Opponents fear the aging reactor will fail, spewing radiation across a heavily populated area. And they note that the main evacuation route is a narrow road that is routinely congested.

AmerGen spokeswoman Leslie Cifelli said yesterday's decision supports points the company had been making since it sought a new license.

"It shows that what we had been saying has been proven true, and that we should be extended for another 20 years," she said.

Neil Sheehan, an NRC spokesman, said the decision was a critical step in AmerGen's quest for a new 20-year license. The agency is scheduled to issue a final decision on the license request on Jan. 22, but appeals by opponents could push that date back.

One other regulatory hurdle remains: approval from the state Department of Environmental Protection for the company's coastal land-use plans over the next 20 years. A decision is expected by the end of the month, Cifelli said.

The plant, with a boiling water reactor whose design is considered obsolete, would be 60 years old at the end of the license its owner is currently seeking.