In a 36-page opinion, US District Judge Florence Marie Cooper said the Navy must now abide by a previous order which outlawed the use of submarine-hunting sonar in areas off the coast of California known to be populated by whales.

Environmental groups say the equipment is potentially harmful to marine mammals, citing cases in the Bahamas and Canary Islands where sonar has been linked to mass deaths of whales.

Last month Bush granted an exemption to the Navy over use of sonar, arguing it was vital for military preparedness exercises which were in the "paramount interest of the United States."

The decision allowed the Navy to ignore a January 3 injunction requiring it to "monitor for and avoid marine mammals while operating high-intensity, mid-frequency sonar during ... naval exercises."

In her ruling, Cooper suggested Bush's attempt to skirt the earlier court order was "constitutionally suspect."

She also dismissed the argument put forward by the Navy that the lives of its sailors depended on being properly skilled in hunting submarines from hostile nations.

"The Navy's current 'emergency' is simply a creature of its own making, i.e., its failure to prepare adequate environmental documentation in a timely fashion," Cooper wrote.