PEARL HARBOR — A temporary restraining order on the military's use of a certain type of sonar during Rimpac warfare exercises near Hawai'i damages the authenticity of the training, top Navy officials said.

Vice Adm. Barry Costello, commander of the U.S. 3rd Fleet, said yesterday that deploying sailors to sea without training them to use active sonar would be akin to tying one arm behind their back. He said using sonar to track submarines is a skill that deteriorates with a lack of practice.

"The threat for the future is diesel submarines, and they are proliferating in the Western Pacific," Costello told The Associated Press. "I know active sonar is the only effective means today to track and target diesel submarines."

Active sonar finds things by sending out pulses of sound to discover what the sound bounces off of, while passive sonar involves listening to and analyzing the noises that are already there.

The Navy estimates nations in the Western Pacific own at least 140 diesel submarines. The newer models of diesel submarines are quieter and can travel longer distances without surfacing, making them more difficult to detect.

On Monday, U.S. District Judge Florence-Marie Cooper had issued a temporary restraining order out of Los Angeles barring the Navy from using the high-intensity, "mid-frequency active sonar" allegedly harmful to marine mammals.

The use of sonar in the Rim of the Pacific 2006 exercises off Hawai'i was set to start Thursday.

The order, sought by environmentalists, came three days after the Defense Department granted an exemption that temporarily relieved the Navy from the requirements of the federal Marine Mammal Protection Act.

But Cooper based her order on a different set of federal laws, the National Environmental Policy Act.

Cooper wrote that the Navy's failure to prepare an environmental impact statement or take a "hard look" at the potential environmental impact of war games was an "arbitrary and capricious" violation of that act.

Costello said in a statement issued late Monday that participants in the multinational exercises will instead try to find submarines by listening with passive sonar and searching for them visually from aircraft and the surface of ships.

But to be effective, sailors must be proficient in finding submarines using active sonar from ships, helicopters, airplanes and submarines, he said.

Adm. Gary Roughead, who commands both the U.S. Pacific Fleet, said anti-marine warfare is the fleet's top war fighting priority.

"Being able to exercise and operate our active sonars is key to our proficiency in that critical warfare area," he said.

In her ruling, Cooper also ordered the parties to meet to discuss mitigation measures to avoid further litigation.

Cooper's order was to remain in effect until July 18, when a hearing will be held on whether to replace the temporary restraining order with a preliminary injunction. Lawyers were ordered to report by July 12 on the results of their meeting.