WASHINGTON, Jan. 14 -- Bowing to renewed concerns about terrorist attacks, Panama authorities said today that they were beefing up security to protect a British ship carrying radioactive cargo through the Panama Canal this weekend.

"The vessel is a visible target for any group that wants to make a statement," Jorge Quijano, director of maritime operations for the Panama Canal Authority, said in an interview today.

Environmental groups fear that the ship, the Pacific Swan, carrying high-level waste to Japan from France, is vulnerable to terrorists who could board and dislodge or rupture the casks with the waste, threatening a potentially catastrophic release of radioactivity.

Two years ago, when the first shipment of radioactive waste passed through the canal, Greenpeace, the antinuclear group, boarded the vessel to show how easy a terrorist hijacking would be.

Since then another shipment has transited the canal without incident.

But now that the United States has given Panama control of the canal, Panamanian authorities have decided to provide what they described as "greatly enhanced protection" for the new shipment.

Panamanian security forces will board the Pacific Swan as it enters Panamanian waters and take control of security and escort vessels. If necessary, Panama will also provide security from the air, Mr. Quijano said.

"This is definitely the most secure vessel to pass through the canal since Jan. 1," he said, referring to when Panama took over the canal.

Most of the pressure to increase security came from the Nuclear Control Institute, a group in Washington that seeks to limit the spread of nuclear weapons. The group has been monitoring the shipments, which are tied to nuclear power plants in Japan.

The waste is the spent fuel from nuclear power plants in Japan from which the plutonium and uranium has been recovered in France. British ships will make two trips a year through the canal to return the waste to Japan for 15 years, the president of the Washington group, Paul Leventhal, said.

"The consequence of a release of radioactive waste would be long lived," Mr. Leventhal said in an interview. "The contamination would be very hard to clean up, and it could render the canal inoperable and the surrounding areas uninhabitable."

Mr. Leventhal was in Panama at the government's invitation to monitor the Pacific Swan's passage. He said he attended a security session this morning with representatives of the canal authority; British Nuclear Fuels Ltd., whose subsidiary owns the ship; and the Japanese nuclear industry.

Any problem with the ship would be a blow to the industry, which has come under rare public criticism since Japan suffered its worst accident in September. One worker was killed and scores of people were exposed to radiation when workers set off an accidental chain reaction at a plant in Tokaimura.

The industry is counting on France's continuing to reprocess the fuel until it builds its own reprocessing factory. But the new criticism of the industry may threaten those plans.

Although Panama has no new intelligence that predicts a terrorist attack, American officials have said they have worried through much of this decade that a possible narcotics-terrorist plot from Colombia would try to seize the canal.