The environmental group Greenpeace, better known for marshaling forces on the antipollution battle front, has become a defense contractor.

For two years, the group has held contracts affiliated with a project to increase access to the Mayport Naval Station near Jacksonville, Fla., for the Trident nuclear submarine.

Lest anyone get the wrong idea, Greenpeace officials hasten to note that their piece of the action is aimed exclusively at defending theatened sea turtles.

In an unusual marriage of frequent adversaries, Greenpeace holds U.S. Army Corps of Engineers contracts to patrol beaches near the Trident project site, keeping an eye out for turtle nests that might be buried or destroyed in the process of dredging a channel for the missile-bearing subs.

"It's a strange partnership," said Bruce Jaildagian, Greenpeace's international coordinator for sea turtles. "But our beach patrol monitors that area voluntarily all summer long anyway."

Corps contractors are dumping dredged sand on Amelia Island, about 20 miles north of Mayport, to rebuild eroded beaches. The turtle problem arises because the work coincides with the nesting season, when sea turtles crawl onto the beach to bury their eggs.

Federal and state laws prohibit the destruction of sea turtles or their eggs, so the Corps needed a contractor to spot the nests and move them out of harm's way. No easy trick, this: Among other things, the workers have to have licenses to work with endangered species.

Dan Malanchuck, a Corps official in Jacksonville, said Greenpeace was by far the lowest bidder. "The advantage in this case is that they were doing the work anyway, so we're covering their expenses," he said.

Jaildagian said Greenpeace won two contracts for Amelia Island, totaling about $11,000, and holds a similar Corps contract near Jacksonville for about $1,000.

"Because we're a nonprofit organization, no one can match our bid," he said.

The turtle nests are moved to protected hatcheries in state parks and on private land. Greenpeace volunteers check the eggs every three hours at the end of the incubation period and hand carry the hatchlings to the sea.

The group used some of its contract payment to buy an all-terrain vehicle for the beach patrol and to reimburse turtle-seekers for gasoline, Jaildagian said.

And at the end of the year, when for-profit contractors might be rewarding their stockholders, "we throw a party for the volunteers," he said.