The National Marine Fisheries Service is seeking a permit to suspend 48 loggerhead sea turtles, a threatened species under federal law, in cages near an offshore oil platform that is to be blown up.

The object is to see how such underwater blasts affect sea turtles, according to a scientist involved in planning the experiment. But the proposal has already drawn strong protests from conservation groups, who contend that the proposal makes a mockery of laws to protect endangered species.

"We feel this is a mistake," said Carol Allen, director of a Houston conservation group called HEART, which has spearheaded efforts to protect sea turtles along the Gulf Coast. "One loggerhead already has been killed {in an experiment} to establish the lethal zone, and we object to repeating it."

Ed Klima, director of the marine fisheries service laboratory in Galveston, Tex., said the experiment is aimed at improving protection for sea turtles by refining federal guidelines that oil companies must follow when removing offshore platforms.

"We have no intention of killing sea turtles at all," he said. "We will just see if there is any impact to their physiology and stamina for swimming."

Klima said the loggerheads would be placed in cages about 500 yards from the platform, well outside the 200-yard range that scientists believe is the lethal area. Red-ear turtles, a freshwater species that is not endangered, will be placed closer, some strapped in cages with their bellies toward the blast.

After the detonation, the turtles will be retrieved and the dead ones autopsied. Live animals will be The object is to see how underwater blasts affect the turtles.

checked for physical injury and tested to measure physiological changes, such as alterations in blood chemistry or navigational ability.

Klima said the experiment, financed by the Interior Department's Minerals Management Service, will provide useful data for the dismantling of offshore oil platforms.

The platforms typically are loosened by explosives, then lifted with cranes and taken ashore to be dismantled. In recent years, however, scientists have accumulated evidence that the explosions coincided with high rates of turtle and dolphin beachings.

Conservation groups contend that the government already has sufficient evidence that the explosions are affecting sea creatures, and should be researching alternative methods of dismantling the platforms or ways to shoo sea creatures away before setting off explosives.

"Once you start granting this kind of permit, it goes on forever," said Lynn Davidson of Greenpeace. "You have to test different kinds of explosives, at different depths, with different kinds of ocean floors. And then what? Do you start putting dolphins in cages, or manatees?"

Allen said that experiments in using low-frequency sound waves to repel sea creatures have proved promising in Florida, and Davidson said that laser technology could be explored as a way of removing drilling platforms without explosives.

"I'm a biologist. All I know is what the oil industry tells me," said Klima, who said energy firms have determined that there is no adequate technology other than explosives to remove the platforms.

A spokesman for the U.S. Fish and Wildlife Service, which administers the Endangered Species Act, said the agency would rely on the advice of the marine fisheries service in deciding whether to allow the use of loggerheads in the experiment. "They advise us as to whether this activity would jeopardize the species," she said.

An official at the fisheries service said the request is under review.