The last boats of the U.S. tuna fleet were scheduled to set sail for their traditional Pacific fishing grounds Saturday, completing a flotilla that till Thursday had been tied to the wharves here in a three-month-long protest of Federal restrictions on the number of porpoises that the tuna fishermen may kill.

Those boats steaming out Saturday to join the 17 seiners that sailed Thursday would have gone today save for the superstition against ever beginning a voyage on Friday - anc certainly not on a Friday the 13th.

The boats that sailed Thursday weighed anchor within minutes of a vote by fishermen that ended the boycotts and a three-day rift between seamen and their skippers.

Owners of the boats and members of the Masters and Mates Association, who captain them, agreed earlier this week to return to work pending approval of a bill by Rep. John N. Murphy (D-N.Y.), chairman of the House Merchant Marine and Fisheries Committee, that would relax the porpoise kill restrictions that brought the fleet steaming into port in protest.

But the rank-and-file members at first refused to man the boats.

"All we wanted was a chance to have our say," said Pat Tague, a crewman aboard the Aquarius, which sailed Thursday, "I wanted to go to sea; but they shouldn't have tried to leave without asking the crews what they wanted to do."

The fleet went back to sea under terms of the restrictions that the fishermen had been protesting, but industry spokesman said the action was taken as a sign of support for Murphy's bill.

At issue in the protest is the number of porpoise that may be killed by tuna fishermen. The porpoise, also called dolphin, swim with the tuna, and fishermen spotting them can be reasonably sure of a school of tuna underneath. But the air-breathing creatures often become tangled in the tuna nets and drown. Environmentalist groups have long advocated that tuna fishermen take all steps possible to avoid killing the intelligent, playful porpoises.

Successful environmentalist lobbying brought about earlier this year - after months of hearings both here and in Washington - regulations by the National Marine Fisheries Service limiting the number of porpoise that may be killed in 1977 to 59, 050 and banning totally any deaths of a porpoise species known as eastern spinner.

It was those regualtions that brought the fleet back in February to protest, the seiners steaming home to San Diego and Puerto Rico and sitting idele at dockside.

In this months since, tuna canneries here have laid off workers, planeloads of fishermen's wives have flown to Washington to lobby members of Congress for relaxed restrictions, and the men themselves have been idle.

"We've never had our nets in such good shape before," said one grizzled old fisherman earlier this week. "That's all we've had to do - keep the boat spic and span and keep the nets mended."

Murphy's legislation, introduced in the House after the New York congressman visited here for several days of discussions with skippers and owners, would give the tuna fleet a kill quota of 79,800 porpoise for the rest of this year and would allow some deaths of eastern spinner porpoises.

Industry spokesman August Felando says such a quota is reasonable. The earlier figure by the fisheries service, he said, was too low to be met economically and the ban on eastern spinners impossible to keep because porpoised look very much alike underwater.

Environmentalists, primarily an orgainzation known as Save the Dolphin, fought for years to have limits placed on porpoise deatsh in tuna fishing, feeling that continued killing would deplete the species.

Though the boycott is now over and fishermen are steaming for their fishing grounds off South America, the effects of the protest will become apparent this summer.

Because the canneriew went three months without fish, the price of a can of tuna is expected to jump at least 20 cents, and probably much more.