WASHINGTON (AP) -- The Navy says it won't perform high-volume sonar tests that could be harmful to whales and other marine life when it conducts a military exercise off the New Jersey coast.

Environmentalists welcomed the decision, which marks an escalation in a dispute over whether an effort by the Navy to test and deploy advanced underwater detection systems is dangerous to the huge mammals.

In a statement reported in The Washington Post on Saturday, the Navy said its Littoral Warfare Advanced Development test 45 miles offshore will go ahead this coming week but will ''not include active acoustic sources.''

Many scientists believe that whales and other marine mammals can be harmed by the extremely high-decibel sounds emitted by the Navy's new sonar systems. The animals rely on their hearing for navigation and can suffer hearing loss and other problems because of the sonar noise, which can be greater than a 747 jetliner at takeoff.

Two months ago, a dozen whales beached themselves in the Bahamas a day after the Navy used the intense sonar in exercises there.

Earlier this month, the Commerce Department's National Marine Fisheries Service sent a letter to the Office of Naval Research complaining that the Navy's assessment of potential environmental damage was inadequate.

Joel Reynolds, an official with the Natural Resources Defense Council, said the Navy's decision to cancel the tests marks a significant change.

''We think this is very important because the Navy has now been told it cannot simply reserve a vessel, schedule an exercise and proceed without worry of environmental impacts when dealing with low-frequency sonar systems,'' he told the Post.