A federal judge has temporarily struck down a U.S. government permit authorizing Japanese salmon fishing in Alaskan waters, citing the alleged threat to marine mammals unintentionally snared in invisible fish nets dropped into the ocean.

The decision late Monday by U.S. District Judge Norma Holloway Johnson will halt the annual salmon fishing season of 129 Japanese vessels in the Bering Sea and North Pacific Ocean. It is expected to displease the Japanese government, which agrees not to fish for salmon outside a 200-mile U.S. conservation zone in exchange for right to catch the fish near Alaska for 50 days starting every June 10.

Johnson, pondering the economic and diplomatic costs, ruled that "the interests of the marine mammal populations at stake in this case outweigh those of other interested parties. This is especially apparent when the public interest in protecting the environment is considered."

Her ruling stems from lawsuits filed by environmental and Alaskan fishing groups, which contend that the Commerce Department permit issued to the Japanese in May ignored a 1972 law aimed at conserving porpoises, seals, sea lions and other marine mammals that get trapped and drown in the nets used to catch salmon.

The order becomes effective after the groups post bond to cover the damages of Japanese fisheries in the event the permit is judged valid in a full court trial. A hearing to set the bond is expected in the next few days.

Jay Johnson, assistant general counsel for fisheries at the Commerce Department's National Oceanic and Atmospheric Administration, said the agency plans to appeal the ruling.

John A. Hodges, a Washington lawyer representing a Japanese trade association of salmon fishing vessels, said the industry spent $40 million in preparation for the season and is "very distressed" by the withdrawal of the permit less than a week after operations began. He predicted "serious concerns" in Tokyo.

"If they can't operate outside the zone and they can't operate inside, where's the benefit for the Japanese?" he asked.

The 1978 agreement permiting Japanese salmon fishing was qualified by Congress the same year. Foreign vessels would have to obey the Marine Mammal Protection Act (MMPA), which prohibits the killing or injury of the animals by nets. A waiver was possible to allow for accidental deaths or injuries, but not to the "disadvantage" of depleted species, according to Congress.

Japan has been granted permits since 1981, which set quotas for the number of Dall's porpoises, northern sea lions and northern fur seals it is allowed to destroy unintentionally.

When the Commerce Department issued a new permit May 14, it only restricted injury to porpoises during the next three years, despite the threat to northern fur seals around the Pribilof Islands in Alaskan waters whose population has declined by one-third since the mid-1970s.

In her ruling, Johnson noted that the permit signed by Commerce Secretary Malcolm Baldrige is "clearly contrary" to MMPA because he has failed to determine whether any of the marine mammals expected to be snared by nets will be "disadvantaged" from a population standpoint.

"It is, by statutory definition, impossible for a Pribilof seal to be taken without disadvantaging the stock," she said.