WASHINGTON — The Supreme Court appeared divided today over how to resolve a long-running dispute over whether environmental laws may be used to limit the Navy's use of sonar to protect whales.

The court heard arguments in the Bush administration's appeal of court rulings that restrict sonar in submarine-hunting naval training exercises off the Southern California coast. Sonar can interfere with whales' ability to navigate and communicate.

The training is "vitally important" for sailors who may be deployed around the world in search of enemy submarines, Solicitor General Gregory Garre told the justices. Garre said there is scant evidence over 40 years of exercises off the Pacific Coast that the Navy's sonar harms whales and dolphins.

Richard Kendall, a lawyer for the Natural Resources Defense Council, said the sonar's piercing sound was comparable to the noise of a jet engine magnified 2,000 times in the courtroom.

A species of whales called beaked whales are particularly susceptible to harm from sonar, which can cause them to strand themselves onshore, Kendall said.

The case left one justice, Stephen Breyer, wondering how a judge should balance national security concerns and environmental interests.

"You are asking us who know nothing about whales and less about the military to start reading all these documents to try to figure out who's right in the case where the other side says the other side is totally unreasonable," Breyer said.

The exercises have continued since the 9th U.S. Circuit Court of Appeals in San Francisco ruled in February that the Navy must limit sonar use when ships get close to marine mammals.

Kendall told the justices that the Navy is managing under the restrictions, saying eight of 14 planned exercises have been completed since the restrictions took effect.

This round of training is scheduled to be completed by January.

Separately, the Navy has agreed to similar limits on anti-submarine training off the coast of Hawaii to settle a lawsuit.

But Garre said the issue for the court is whether federal judges should have stepped in to force changes to the training when the government's first environmental assessment found there was little prospect of harm.

The Navy's own environmental assessment of using sonar during the 14 training exercises off the California coast found that it could disturb or harm an estimated 170,000 marine mammals, including possible temporary hearing loss in at least 8,000 whales.

The administration also says the president has the power to override federal court rulings on environmental laws during emergencies that include harm to national security. The Navy says it already has taken steps to protect beaked whales, dolphins and other creatures and is balancing war training and environmental protections.

Justice David Souter ridiculed the idea that the administration could declare an emergency to try to get around complying with environmental laws. The Navy opted not to conduct a more rigorous environmental study, an environmental impact study, before beginning the long-planned exercises, Souter said.

"If there's an emergency, it's one the Navy created simply by failing to start EIS preparation in a timely way," he said.

Justices John Paul Stevens and Ruth Bader Ginsburg also suggested that the Navy could have avoided the court fight by producing the impact study before the exercises began.

Justice Samuel Alito suggested that he found little evidence in the court record that the marine mammals would be harmed by the sonar use.

Alito also said there was "something incredibly odd" that a single federal judge, who issued the first order against the Navy in this case, would be able to force changes in the exercises. Chief Justice John Roberts and Justice Antonin Scalia also appeared supportive of the government's case.

An injunction by U.S. District Judge Florence-Marie Cooper in Los Angeles early this year created a 12-nautical-mile no-sonar zone along the coast and ordered the Navy to shut off all sonar use within 2,200 yards of a marine mammal.

The 9th Circuit sided with the lower court and said the Navy must abide by the injunction. However, while the litigation was under way, the appeals court gave the Navy permission to use sonar closer than the restrictions allow during critical maneuvers.

The case is Winter v. Natural Resources Defense Council, 07-1239.