In less than four days, more than 1,300 boats from the United States have turned this drab industrial port into a giant Caribbean yacht club of the kind that disappeared when socialism came to Cuba 20 years ago.

As far as the eye can see, motor launches, lobster boats, yachts, antennas and fishing rods bob up and down in the sun. Boat owners clamber up and down on deck, yell and swap drinks and stories about what may be one of the greatest adventures of their lives -- the rescue of friends and relatives who want to leave the island.

At the entrance to the harbor, a constant procession of boats still files in. And, as in every port in the world, a brisk trade in goods and services for the sailors has started, although here it is strictly controlled by the government.

Official boats swing by to sell food, drinks and even official souvenirs. "The U.S. economic blockade of Cuba has been broken here," exclaimed the official newspaper Granma today, in reference to the 18-year-old U.S. embargo on trade with Cuba. "There is a great demand for Habana Club rum and other Cuban products."

As the Cubans see it, this still may only be the beginning of the exodus. Today for the first time the Cuban government indicated openly that it envisions a purge of its society, letting go of most of its dissidents, whatever the numbers may be. Today it openly said what had up to now been only indirectly implied -- that anyone who wants to leave can go.

"Passports and safe conduct will be given to all the lumpen who request it," announced the official newspaper Granma on its front page. "They are all dissidents and they have the same rights. Any discrimination would be unjust and unconstitutional."

The term lumpen, short for lumpen proletariat, has become the standard phrase here to describe the 10,500 people who stormed into the Peruvian Embassy three weeks ago. Although the government has openly encouraged the Cuban exiles in the United States to pick up these people, officially its policy was limited to allowing the exit only of the 10,500 and other Cubans who already have relatives in the U.S.

Significantly, well placed Cuban sources here said that today's announcement was also a green light for people involved in pending criminal cases who have traditionally been refused exit visas.

Last fall, Cuban police launched a severe crackdown on growing crime in Havana and other major cities. It was aimed at destroying the network of people who run the black market resale of stolen goods, the illegal gambling, speakeasies, cock fighting and marijuana sales.

Some members of the criminal underground awaiting trial had reportedly fled into the Peruvian Embassy, but they were a small minority. Although the government here has insisted on calling all the embassy refugees "delinquents," it became clear that they were people from all walks of life, ranging from respectable Communist Party members to professionals who are members of the clandestine counterrevolutionary network.

The Cuban sources said that the government clearly wants to rid itself not only of opponents but also of "known criminals and two of them have just left, one of them a member of a marijuana ring and one the leader of the stolen car ring."

Here in Mariel, the flow of buses bringing refugees continues in the same tightly controlled and low-key manner in which it began four days ago.

One crew member of a U.S.-based boat said that they "negotiate" with the Cubans to take both family members and refugees from the Peruvian Embassy. According to Granma, about 1,522 people were inside the embassy building yesterday.

But the officials dealing with the refugee movement are clearly overwhelmed by the logistics involved in locating, transporting and providing documents for the people leaving.

Following the government's announcement yesterday that U.S. planes could also come to Cuba to pick up refugees, the newspaper said that 32 U.S. planes had already requested landing permits. But they had been asked to wait for the authorities to deal first with the large backlog of boats already waiting.

The waiting time for the boats is now running into three days and the Cubans today opened a motel in Mariel and at the nearby Salado Beach for waiting crew members.

Yesterday, according to Granma, another 722 people left by sea. Among some diplomats here who have long watched President Fidel Castro's political style, the feeling is that after today's blanket permission for everyone to leave, he is forcing the U.S. government to sit down and negotiate.

"Castro knows that a few hundred thousand people may leave and he knows there is panic in Washington," one key diplomat said. "Now he seems to be forcing the U.S. to start talks again."

Cuba feels that in the past year the Carter administration has turned the steadily improving relations between Havana and Washington to hostile ones and that the new dialogue has been cut off. As proof of the hostility, high Cuban officials point to the resumed surveillance flights, the U.S. blocking of a Cuban seat on the United Nations Security Council, a publicity campaign denouncing Cuba's alleged support of revolutionaries in El Salvado, and the three-week military maneuvers in Caribbean that began on May 8. A Cuban official has described these maneuvers, which involve landing 5,000 U.S. troops on the Guantanamo military base in Cuba, as "extremely dangerous."