The district court on Jan. 3 barred the Navy's use of powerful submarine-hunting mid-frequency active radar within 12 miles (19.31 km) of the coast, protecting a strip of water that is habitat for whales, dolphins and other marine mammals.

The court also imposed other restrictions, including a stipulation that the Navy switch off sonar if marine mammals are spotted within 2,200 yards (2,012 metres) of sonar vessels.

But Bush intervened, citing the national security necessity of last month's Navy training off the California coast, and exempted the Navy from the environmental laws at the heart of the legal challenge.

Environmental groups led by the Natural Resources Defense Council (NRDC) have documented cases of mass whale strandings and deaths they say are associated with sonar blasts that also sometimes cause bleeding from the eyes and ears.

While Cooper expressed "significant concerns" about the constitutionality of Bush's exemption, she avoided ruling on it. But she said the previous injunction remained in place.

"By leaving the injunction in place, the Navy may continue with its training exercises while limiting negative effects on marine life," she wrote.

Joel Reynolds, a senior attorney for the NRDC, hailed Cooper's decision.

"We're very pleased," he said. "The president's attempted end-run around Congress and the order was illegal and invalid."