WASHINGTON

A federal judge Thursday severely limited the Navy's ability to use midfrequency sonar on a training range off the southern California coast, ruling that the loud sounds would harm whales and other marine mammals if not tightly controlled.

The decision is a blow to the Navy, which has argued that it needs the flexibility to train its sonar operators without undue restrictions. In her decision, District Judge Florence-Marie Cooper said the Navy could conduct productive training under the limitations, which she said were required under several environmental laws.

Cooper banned the use of the sonar within 12 nautical miles of the California coast, expanded from 1,100 yards to 2,200 yards the Navy's proposed "shut down" zone in which sonar must be turned off whenever a marine mammal is spotted, and required monitoring for animals before and during exercises.

Navy spokeswoman Cindy Moore said the Navy was reviewing the ruling.

Active sonar has been used for decades to detect submarines, but marine specialists began to connect mass strandings of whales with the loud sound blasts only a decade ago.

The plaintiff in the lawsuit, National Resources Defense Council, has also criticized the Navy's plan for a sonar training range off the North Carolina coast. The Navy is conducting an environmental analysis of the proposed 625-square-mile range, where Norfolk-based ships would practice hunting subs.

Critics claimed the Navy's initial assessment in 2005 of the possible damage to mammals was cursory, and its plans to mitigate harm were deficient.

Michael Jasny, a senior policy analyst for NRDC, said the California ruling is sure to affect the North Carolina proposal. "The court finds the existing standard mitigation scheme is woefully inadequate, and this would be true virtually regardless of where they're operating," Jasny said. He said the council will keep pressure on the Navy.

Virginian-Pilot staff writer Kate Wiltrout contributed to this report.