GUANABACOA, CUBA, SEPT. 10 -- An aging tugboat crumbled beneath its terrorized passengers on the high seas. By the survivors' account, water pounded against them as weary men, women and children gasped for air and tried to keep afloat. Mothers desperately tried to tread water with one hand while clutching infants, then finally lost their grips and condemned their babies to death by drowning. Help was at hand on other boats, but they turned away.

The story is not among those of the 20,000 Cuban raft people who set out to sea over the last month after President Fidel Castro opened the doors to emigration. Rather, it is the survivors' version of what happened earlier, when Castro's Communist government attempted to crack down on those attempting to flee.

After Friday's accord with the United States calling on Cuba to halt the exodus of raft people, the story of 68 passengers aboard the tugboat 13th of March looms as a precedent for what might happen now that Castro has pledged to close the door once again.

During the predawn hours of July 13, three tugboats were dispatched from the port authority of Havana to follow the commandeered 13th of March out to sea. By the account of interviewed survivors -- disputed by Castro and the official press -- when the tug was seven miles offshore the authority's boats pummeled passengers on its deck with water cannon, then systematically sank the boat by ramming it in unison until it broke apart. Crew members refused to help survivors out of the water. Two Cuban military gunboats stood a few hundred yards away while the demolition was underway.

At least 37 passengers from the 13th of March drowned, while 31 survivors lived to retell a story that circulated throughout this island nation and prompted the Cuban migration crisis of 1994.

Over the succeeding three weeks, three other passenger boats, a military craft and an airplane were commandeered. Street demonstrations erupted, culminating Aug. 5 in a Havana riot in which civilians killed two policemen and gravely injured a third. On Aug. 6, Castro announced a new policy lifting all restrictions on emigration by sea. Many here are calling the tugboat saga "Cuba's version of Tiananmen Square."

Six survivors from the 13th of March recounted their ordeal during interviews this week here and in the neighboring town of La Magdalena, near Havana.

"It all started with us," said Maria Victoria Garcia, 28, who until 4 a.m. on July 13 was the mother of a 10-year-old boy, Juan Mario. "What happened that morning was premeditated murder. It was a massacre."

The 13th of March was a wooden 115-year-old tug that was docked in Havana. Two tugboat captains from Guanabacoa who worked at the port, Fidencio Ramel Prieto, 51, and Raul Munoz Garcia, 22, met secretly in early July and agreed to organize a small group of family members, sneak them aboard the recently renovated boat and, under cover of darkness, set out for Florida. By the time the group entered Havana port at 3 a.m., it had swollen to an unwieldy 68 people, varying in age from less than 12 months to 60 years.

Ramel was deputy director of the port as well as secretary in the labor division of Cuba's Communist Party, and among the nation's most experienced mariners. He had been chosen to fly to the Netherlands in 1987 to take possession of five new tugboats purchased by Cuba to replace its aging fleet. Three of the tugs he guided across the Atlantic in 1987 were used to hunt him down on July 13 and crush his 51-foot craft into splinters.

Ramel and Garcia both knew that security at the port was minimal from midnight to dawn and that they would have few problems sneaking onto the 13th of March.

"Nobody tried to stop us," said Jorge Cuba Suarez, 24, a neighbor of Ramel's family here. "After we got out of the port, another tugboat started following us. They could have turned us back at any time but they didn't." He said Ramel ordered everyone to remain in the hold until they had reached international waters.

"We spent about an hour down below and then Raul yelled for all women and children to come up to the deck," said Maita Tacoronte Vega, 36, of La Magdalena. "I went up and could see that two tugboats were right next to us. Ramel wanted us on deck to show them we were just a bunch of women and children."

Tacoronte said the tugboats began "shooting water at us" from water cannon mounted atop their helms, and Ramel shut down his boat's engine.

Then, without warning, one tugboat rammed the 13th of March from behind. "I was standing right there when it happened," recalled Maria Victoria, who is Ramel's daughter. "The force knocked everybody down. We had to grab anything we could just to keep from falling into the water."

Another tug punched a hole in the hull of the 13th of March, the survivors said, and a third joined in the ramming.

"The entire deck buckled. It separated completely from the hull. I started sliding into the water and I remember thinking, 'We're all going to die,' " Maria Victoria said.

"Most of the men were still down below," said Daysi Martinez Fundora, 26. "We all started screaming, 'Please, mother of God! We're all Cubans. At least save our children!' But the crew members on the other boats just stared at us."

In less than five minutes the 13th of March had sunk, with more than two dozen people still hiding in its hold. Tacoronte said she and other mothers clutched their children while grabbing anything afloat to keep their heads above water.

"I don't know why, but they kept shooting water at us. I couldn't open my mouth to breathe." Tacoronte said she refused to let go of her 3-year-old daughter, Milena, who sat on her lap throughout the interview.

Maria Victoria said she kept one arm wrapped around 10-year-old Juan Mario for about 30 minutes, while holding onto a large wooden box floating in the water and while 10 other people flailed about trying to maintain their grip on it.

Someone's foot hit Maria Victoria's arm, causing her to lose her grip on Juan Mario. "He disappeared. Someone screamed, 'Grab Juan Mario. He's going down!' But he was gone. I never saw my little boy again," Maria Victoria said, adding that she now is taking prescription tranquilizers and receiving psychiatric treatment.

Jorge Luis Garcia said the survivors pleaded with crew members on the three tugboats to rescue them, "but they just stared at us. One man stood on the deck with his arms crossed. I couldn't believe it. They were trying to make us drown."

At about 5 a.m., two Cuban navy gunboats moved in and fished 31 people from the waters. They circled for six hours without finding any other survivors, then headed back to Havana. Capt. Ramel and at least 15 other men perished, along with four boys, three girls and 13 women.

Cuban human rights workers say they are still trying to interview survivors to compile a full list of everyone on the boat. "There might be more dead but we won't know until we've visited every survivor's home," said Elizardo Sanchez Santa Cruz, president of the Cuban Commission of Human Rights and National Reconciliation.

Interviews have been difficult because many of the male survivors were kept in jail after their rescue. Raul Munoz remains in prison. Garcia said he was jailed for 12 days. Maria Victoria's brother, Ivan Suarez, said he was held for 22 days. Women and children were allowed to go home after a few hours of questioning.

Official accounts of the incident printed in the government newspaper Granma said the 13th of March sank after an "accident" in which one of the government tugboats collided with it while attempting to rescue the passengers.

"If they had tried to rescue us my boy would be alive today," Maria Victoria said.

Granma confirmed the water cannon were used but said they were directed at the boat's smokestack and helm in an attempt to shut down its engine. Granma blamed the accident on Ramel and Munoz while quoting Munoz from prison as saying that Ramel "knew the boat was unseaworthy" but had deliberately risked setting out to sea.

Granma also said the rescue attempts were made difficult by rough seas that morning. All survivors interviewed said the sea was calm. Maria Victoria's parents compiled a scrapbook to chronicle the deaths of more than a dozen family members who were passengers. Pasted onto one page are the official weather reports from July 13 as well as the day before and day after. All described clear weather and calm seas.

In an Aug. 24 speech, Castro called the disaster the first incident in the current migration crisis but said "it remains proven that the authorities had absolutely nothing to do with this accident."

Ester Suarez, Ramel's wife, disputed government assertions that her husband was a "counterrevolutionary" and a traitor. "He was a senior member of the Communist Party. He was devoted," she said, pulling out Ramel's party membership booklet. "Look, Fidel signed his booklet personally."

"I think Fidel really believes this was an accident. They have lied to him," Maria Victoria said. "He needs to know the truth, that this was murder." She said Communist Party officials had offered to give her a new house, fully furnished, if she would agree to keep quiet about the incident, but she refused.

On Aug. 3, two days after Ivan Suarez was released from jail, he and his mother were returning to Guanabacoa from a shopping trip to Havana. They boarded a 194-passenger ferry, La Coubre, that would carry them past the dock where the 13th of March had been moored.

Suddenly the ferry's engines surged and the boat lurched toward the sea. La Coubre had been hijacked. Two hours later, Ivan and Ester Suarez were in international waters. A U.S. Coast Guard ship pulled alongside and an announcement was made that anyone aboard who wanted to seek asylum would be allowed to travel to a detention center near Miami.

"Ivan looked at me and I told him I could not go. My family needed me at home," Ester Suarez said. "He decided to come back with me."

Seventy-six passengers chose to return to Cuba, where they received a hero's welcome and personal expressions of gratitude from Castro. "In two days, Ivan went from being a prisoner and an example of national disgrace to being a national hero," Ester Suarez said. "This is Cuba."