Drive to stop killing by tuna fleets is given new impetus. DOLPHIN SLAUGHTER

An emotional and enduring dispute over the killing of dolphins by foreign and domestic fishing fleets is boiling up again. Environmentalists are pressing for a reduction in the number of dolphins the federal government allows American fishermen to kill each year while netting tuna. At the same time, they want more pressure exerted on foreign operators.

The United States tuna industry argues that it is operating well within federal strictures and that any change in its fishing methods could bankrupt the domestic fleet. ``It is a complex, emotional issue,'' says David Burney, counsel to the US Tuna Foundation, an industry group.

The debate was given new impetus recently by a graphic videotape. Last year, California biologist Sam LaBudde took a job as a cook on a Panamanian tuna boat. He brought along a video camera.

Surreptitiously, Mr. LaBudde took hours of footage showing what environmentalists call the ``slaughter'' of hundreds of dolphins during fishing off South America. The mammals were killed in the vessel's tuna nets or by winches that hauled the catch aboard.

Emboldened by the tape, environmental groups are renewing a drive for greater protection for dolphins and other porpoises. This week several groups - including the Sea Shepherd Society, the Earth Island Institute, and the Marine Mammal Fund - launched a boycott of canned tuna in the US. Two of the groups also filed a federal court suit in San Francisco, seeking to stop the killings.

``It is an incredible waste of an intelligent marine mammal for corporate interests,'' says Peter Wallerstein, director of the Sea Shepherd Society, a California-based marine conservation group.

The flap over dolphins and tuna nets is unique to the eastern tropical Pacific, an area stretching from southern California to Chile. There, for some reason still a mystery to scientists, yellowfin tuna swim under herds of dolphins. Guided by the presence of the dolphins, fishermen encircle both dolphins and tuna with mile-long nets. The dolphins are let go when the fish are winched in, but some inevitably perish in the process.

Environmentalists claim that 6 million dolphins have been killed since the seining technique began to be used in the 1960s. Last year an estimated 14,000 dolphins were killed by US boats in the netting of 85,000 tons of tuna. Foreign vessels were believed to have killed several times that number.

Under the Marine Mammal Protection Act of 1972, dolphins may not be killed or harassed. But the tuna industry won a provision in 1981 that allows the US fleet to kill up to 20,500 of the mammals each year. In 1984, Congress banned the importation of tuna from any country that does not meet kill rates comparable to those set for the US.

Environmentalists say that quota violates the spirit of the 1972 law, which requires that the number of dolphins killed during tuna netting be reduced to an ``insignificant level approaching zero mortality.'' They want it phased out over four years.

``The intent of the act is not to maximize the gross tonnage of tuna caught,'' says David Phillips, director of the San Francisco-based Earth Island Institute. ``It is to minimize dolphin deaths.''

Industry officials, however, say the quota was set at a level that does not threaten porpoise populations. They contend that reducing the limit would wipe out the 35-boat US fleet, leaving the eastern Pacific exclusively to foreign operators over whom the US has no direct control.

Industry officials maintain that 99 percent of the dolphins netted by US fishermen are safely released. Most US vessels are now monitored by official observers.

Some 290,000 tons of yellowfin were caught by US and foreign fleets in the eastern tropical Pacific last year, most of it by the porpoise-encircling technique. The region produces about 20 percent of the world's white-meat tuna, according to the industry.

Foreign fishermen may pose a bigger problem. The National Marine Fisheries Service says it will start enforcing the embargo against countries whose fleets don't show a ``downward trend'' of kills starting next year. But the agency is giving foreign fleets until 1991 to bring their kill rates down to those comparable with the US - which even some US fishermen believe should be done sooner.