The Navy's use of sonar during maritime exercises may have contributed to the mass stranding of more than 150 whales in Hawaii's Hanalei Bay two years ago, government scientists said.

The National Oceanic and Atmospheric Administration said the finding — along with information from other studies — has led it to ask the Navy to reduce its sonar's power during exercises planned this summer in Hawaiian waters. It also asked the Navy to turn off its active sonar when the whales come within a set distance.

The Navy says it will comply with the agency's requests, but said the report released Thursday did not conclusively show sonar triggered the stranding.

Officials were unable to find other reasons that may have caused the melon-headed whales to swim into the bay on July 3, 2004. One whale beached itself and died a few days later, said Brandon Southall, director of NOAA's acoustics program.

Nearby predators or other factors may have also contributed to the incident, NOAA said in the report.

The Navy uses sonar technology to detect threats and to navigate. Some wildlife advocates believe the sound waves hurt whales, possibly by damaging their hearing or causing them to rise to the surface too quickly and get decompression sickness.

The day before the whales entered Hanalei Bay, six U.S. and Japanese vessels steamed north from the island of Oahu toward Kauai, intermittently using active sonar signals.

NOAA's study concluded the whales — which usually inhabit only deep water — may have heard thee signals and headed into the shallow water.

Lt. William Marks, Navy spokesman at the Pentagon, said the six-hour gap between the last use of sonar and the whales' arrival made it unlikely sonar triggered the stranding.

But environmentalists said the report clearly blamed sonar.

"It adds to a long and growing use of strandings that have been associated with the Navy's use of sonar," said Michael Jasny, senior consultant with the Natural Resources Defense Council in Los Angeles, citing other mass strandings in the Canary Islands, Alaska and Japan.