By GENE MILLER

Speculation arose Friday that the "pirate yacht" that machine-gunned and sank one unarmed fishing boat from Cuba may also have sunk a second vessel.

"That's what the survivors think," said Ed Sweeney, regional director of the U.S. Immigration and Naturalization Service.

A Norwegian freighter rescued four Cubans from a raft and a rowboat before dawn Thursday off the Cay Sal Banks and brought thetas to Miami.

With them was a dead companion, who bled to death when a bullet from an automatic weapon almost tore off his arm.

They told FBI agents here that a "bluish pirate yacht" had caught them at nightfall Monday and riddled their 60-foot fishing boat, Ferro Cemento 119.

Prior to the time they were attacked, according to the FBI, they had seen two other boats in the distance. They believed that one vessel, like theirs, was an unarmed fishing boat from Cuba.

"They heard automatic fire before they were attacked," said Sweeney. "They saw only the vessel that attacked them. They think the attack vessel may have sunk the other one, too.

"It was too dark to see," he said.

Radio Havana did not mention the attack Friday.

The surviving Cubans are from Mantanzas province in northern Cuba. They told U.S. authorities they want to be returned to Cuba.

Sweeney said arrangements are being made. He declined to say where they are staying in Miami. "There is no way that will get out," Sweeney said.

The fishermen have said they do not wish to be interviewed by U.S. reporters, he said.

The FBI said nothing of its investigation Friday. It assumed jurisdiction because of a crime on the high seas - and/or a possible violation of the Neutrality Act.

An anonymous telephone call claimed Thursday that the Cuban National Liberation Front (FLNC) and Brigade 2506 made the attack.

It wasn't the first such assertion. On Oct. 3, 1973, the FL sent a "war communique" to Miami newspapers and radio stations claiming responsibility for the sinking of fishing fleet boats off Cuban Cayo Romano on the northeast Cuban coast.

At that time the Cuban government accused exiles of the attack It said Roberto Torna Mirabal been killed.

A few days later Miami's Replica magazine published pictures of what, it said was material confiscated by exiles aboard the sunken boats. It showed Russian language code and navigation books, as well as electronic gear.