SAN DIEGO — Federal officials issued a permit yesterday for the Navy to use sonar during Rim of the Pacific exercises under way off Hawai'i, sparking protest from environmentalists who say the sonar will harm whales.

Jim Lecky, director of the office of protected resources at the National Marine Fisheries Service, said he is confident the Navy has implemented safeguards that will keep whales and other marine mammals from being harmed by the sonar.

The biennial Rimpac exercises, involving eight nations, 40 ships, six submarines and 19,000 military personnel, began Monday. The sonar exercises will begin next week.

Officials at the Natural Resources Defense Council said they plan to file a lawsuit today in Los Angeles federal court to overturn the permit and block the sonar tests.

Joel Reynolds, senior attorney and director of the council's Marine Mammal Protection Project in Los Angeles, said it "strikes us as absurd" that the sonar tests would be allowed so soon after President Bush declared the area around the Northwestern Hawaiian Islands as a national monument. That status provides protection for marine life and other resources in the area.

"This is one of the unique ecosystems of the world," Reynolds said. "Why should the Navy be allowed to carry on a month of war games here?"

(The naval exercises will take place in waters near Hawai'i but not around the Northwestern Hawaiian Islands.)

Two years ago, during similar naval exercises, 150 melon-headed whales gathered in a shallow-bay off Kaua'i. A federal study concluded that the sonar was the likely cause for the whales' unusual behavior.

The Navy and environmentalists have been at odds for several years over the experimental use of sonar. Several instances of whales beaching themselves have been attributed to the sonar but the scientific evidence is a matter of dispute.

Lecky said he is satisfied that no whales will be hurt during this year's exercises because of the presence of spotters on ships and planes who will warn the Navy to turn off the sonar if whales are seen. Also, "safety zones" have been established where the Navy cannot intrude.

The Navy says the exercises are an invaluable way to train with allies and that the sonar tests are particularly important.

The undersea geography in the Hawaiian island chain contains several channels of "chokepoints" like those of the Strait of Hormuz, the narrow opening in the Persian Gulf.

The sonar tests are meant to see if U.S. and other participating forces can detect stealthy diesel-powered submarines like those being built or purchased by the governments of Iran, China and North Korea.