PEARL HARBOR — The U.S. Navy yesterday filed an emergency motion with the 9th U.S. Circuit Court of Appeals in San Francisco seeking to reinstate active sonar use during Rim of the Pacific naval exercises, an attorney with the Natural Resources Defense Council said.

On Monday, U.S. District Judge Florence-Marie Cooper 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 after the Natural Resources Defense Council and other groups filed a lawsuit.

The use of active sonar in the Rimpac 2006 exercises off Hawai'i was set to start today. Twenty-one ships pulled out of Pearl Harbor yesterday for the exercise scheduled through July 28.

Joel Reynolds, a senior attorney with the defense council, said the Navy in the emergency motion made a "very similar argument as was made at district court — arguing that they were right on the law, and that national security requires them to be able to proceed."

The defense council has to respond by today. Reynolds said he had not completely read through the "quite lengthy" motion, "but I assume it's just asking for the court to act as soon as it can."

The biennial naval exercise this year involves more than 19,000 service members, 35 surface ships, six submarines, 160 aircraft and amphibious forces from the U.S. and United Kingdom, along with Australia, Canada, Chile, Peru, Japan and South Korea.

Cooper said the plaintiffs "have submitted considerable convincing scientific evidence demonstrating that the Navy's use of (mid-frequency active) sonar can kill, injure and disturb many marine species, including marine mammals."

Cooper ordered the Navy and the environmental groups to meet "to determine if an agreement can be reached on mitigation measures."

The sides have until Wednesday to inform the court about the success of such discussions. The injunction remains in effect until July 18.

The Navy and defense council yesterday "were on the phone for some time" trying to reach an agreement, said Hamlet Paoletti, a defense council spokesman.

"We're not opposed to Rimpac, and we're not opposed to active sonar during Rimpac," Paoletti said. "What we're opposed to is the use of active sonar without specific measures that would reduce or eliminate the danger to marine mammals."

Facing mounting legal pressure from groups like the defense council, which sued in 2005 over the use of active sonar, the Navy already had agreed to mitigation measures for Rimpac 2006.

Active sonar emits sound "pings" that travel through water. Passive sonar listens for sound.

Among the mitigation measures were zones of active sonar exclusion ringing the Islands 16 miles out to sea, starting at the point where water depth reaches about 600 to 700 feet.

The exception was Navy plans for intensive "choke point" active sonar use between Maui and the Big Island and two spots between Ni'ihau and Kaua'i.

Also planned for the first time in Rimpac's 35-year history were requirements to reduce sonar output by 6 decibels if marine mammals were spotted within 1,100 yards of a ship, a 10-decibel reduction within 550 yards, and complete elimination of active sonar within 220 yards.

Reynolds said the defense council wants an exclusion zone of about 29 miles — nearly double the earlier proposal — and reduced sonar output during the choke-point training if animals are spotted.

"(The larger exclusion zone) has to do with the abundance of marine mammals within that region and the fact that mid-frequency sonar is loud," Reynolds said. "So you need to establish a sufficient distance (from) the sonar source."

Vice Adm. Barry M. Costello, the commander for Rimpac, yesterday said he could not project what would happen because of the ongoing legal discussions, "but for today, we are barred from using active sonar."

Anti-submarine warfare is one focus of Rimpac, and six submarines — including quiet diesel subs from Japan, South Korea and Australia — are expected to take part in the war games.

To compensate for a ban on active sonar, Costello said, diesel subs "might be a little more active" on the surface and in use of their radars. In addition, surface ships would rely more on visual sighting, radar and passive sonars.

Costello said although passive sonar use and maritime interception and humanitarian assistance training will go forward, he views with "great concern" the active sonar ban.

"If I cannot use active sonar, which has been demonstrated as truly the only way you can ultimately localize a threat like (diesel submarines), then we're going to have problems in the future," he said.

Reach William Cole at wcole@honoluluadvertiser.com.