JUST days before a trip to California, Mexican President Carlos Salinas de Gortari officially poured oil on the troubled waters of a tuna trade dispute with the United States.In an effort to avoid undercutting North American free-trade negotiations, analysts say Mr. Salinas is backing off of a complaint lodged with the General Agreement on Tariffs and Trade (GATT), an organization that regulates world trade. The US began a ban on Mexican tuna last October. Under the US Marine Mammal Protection Act, sale of Mexican tuna in the US is banned - even if canned by third-party nations - because Mexican fisherman are exceeding a dolphin kill quota. But Mexican officials argue that it is unjust for the US Congress to arbitrarily impose its ecological standards on a poor nation. Last month, a GATT panel privately ruled that the US embargo constituted an illegal trade barrier and indicated the US law would have to change. The ruling was to be made official Oct. 8. But environmentalists say a GATT ruling for Mexico would set a precedent that could undermine their efforts on a range of fronts. "If the GATT ruling goes through, international trade sanctions designed to halt trade of endangered species, trade in rare hardwoods, and shipments of toxic wastes could be declared illegal. It would be a very serious blow," says a spokesman with the Earth Island Institute, a San Francisco-based ecology group that pressured the US government to enact the embargo. On Tuesday, Salinas announced as "a show of good faith" that Mexico will "postpone" the final GATT decision and pursue a bilateral solution. Fighting for the Mexican tuna industry is one thing, but being cast as a nation downgrading environmental efforts is another, say political analysts here. It could also assist free-trade critics in the US Congress who say Mexico is too probusiness and too weak on the environment. Salinas also unveiled steps aimed at reducing the kill of dolphins. The measures included: * Possible jail sentences for fishermen who violate proposed, as yet undisclosed, laws relating to protecting marine mammals. * Requiring observers on all fishing boats to collect information about the dolphin kill. * A government grant of $1 million for research into new fishing methods. Homero Aridjis, president of the Group of 100, a Mexican ecology group, called the steps "truly satisfying." The Earth Island spokesmen called them "completely cosmetic. Nowhere in the 10-point plan did Salinas promise to reduce the dolphin kill." Earth Island and other California environmental and labor groups are planning to greet Salinas with demonstrations when he visits San Francisco Sept. 29 and 30.