UNDER a blazing sun the raft is no more than a dot about 20 miles off the coast of Cuba in a calm sea. Overhead a United States Coast Guard C130 four-engine radar plane has spotted it. Two men in the raft are waving frantically."They leave Cuba as an act of desperation," says Jose Basulto of Brothers to the Rescue, a Miami-based volunteer group which rescues rafters or "balseros" escaping from Cuba. Since its founding in May the group has rescued 85 people from homemade rafts and aging boats by flying small planes back and forth over the Strait of Florida between Cuba and Key West. And since the beginning of the year, the US Coast Guard says, the total number of men, women, and children rescued after escaping Cuba is 1,150. That's almost five times the number rescued in l990 and the highest number since the Mariel boat lift in l980, when Fidel Castro allowed 125,000 Cubans to emigrate in private boats. "We have always said that we don't encourage people leaving Cuba by these means," says Mr. Basulto, "not because we are opposed to them getting here to freedom, but because the chances are they will die in the attempt." As economic conditions in Cuba worsen - virtually all consumer goods are rationed - and communism is being discredited worldwide, more Cubans are willing to risk their lives to leave Cuba. Basulto estimates that only 1 in 4 rafters reach Florida. The rest are either captured by Cuban patrol boats or die from lack of water and exposure. Brothers to the Rescue has found 15 empty boats. The Coast Guard plane circles the raft, drops a smoke bomb as a marker and a marine radio, then contacts Guillermo Lares, flying one of three small planes flown by volunteers from Brothers to the Rescue. "We are approximately 10 minutes away," says Mr. Lares, "and on our way." Fidel Castro's Cuba is an island historically dependent on Moscow's support and still committed to socialist doctrine. The recent announcement by President Mikhail Gorbachev that Soviet troops would be withdrawn from Cuba was good news to many Cubans in Miami who wish the worst on President Castro. "Castro is doomed," said Basulto, who was part of the Bay of Pigs debacle 30 years ago. "Someone will kill him. Many elderly men want to go back. They have been waiting for 30 years." Maggie Schuss, who escaped Cuba in l961 and now lives near Miami, said of Castro, "He has taken a beautiful island and destroyed it. If he's going to ask for political asylum now, who's he going to ask? Qaddafi? I want to see Castro hanged." Flying a twin-engine plane, Lares circles the raft and talks with one of the men over the marine radio. The small outboard motor on the raft had stopped running. The two men are fit but sweltering in the heat. The Coast Guard says a Cuban patrol boat is in the area to the east, and that a Coast Guard boat is at least two hours away. Unless a nearby fishing vessel agrees to rescue the two men, the patrol boat could pick them up and take them back to Cuba. If a Cuban patrol boat intercepts any rafters, they are jailed in Cuba for up to two years, according to Brothers to the Rescue. Family possessions are seized and rations books are taken away. The Cuban American National Foundation in Miami recently surveyed 370 rafters who were being held at the Krome Detention Center here, a US government location where all rafters are taken. The majority were men between the ages of 18 and 29, and identified as laborers, drivers, and mechanics. Others were students and technicians. The majority of rafters had spent from one to three days at sea. Usually they left Cuba at night. "We've rescued all kinds of people," said Basulto, "even a woman nine months pregnant. On two occasions we rescued people just as the boat sank." The fishing vessel "Free Spirit" agrees to pick up the sea-bound men and swings around at full power, heading toward the raft. Meanwhile, the Cuban patrol boat has contacted Lares in the plane and wants to know the location of the raft. Lares refuses to reveal the coordinates. "Stay off the frequency," he tells the Cubans. The US Coast Guard says the patrol boat is about 15 miles east. "Our operation is not a political quest," says Basulto, who builds homes in the Miami area as a profession. "It is a human quest." Brothers to the Rescue was founded by Basulto and others in the wake of last year's Flotilla of Cuban Solidarity and Brotherhood, a gathering of dozens of Miami based ships and boats which sailed to a point just off Cuba's 20-mile territorial limit. "We placed a wreath on the water out of respect for those who had died," says Basulto. "And we wanted to do something on a continuing basis." The organization has volunteers from many Latin American countries and is supported by donations from the public. The 40-ft. "Free Spirit" arrows toward the raft as Lares flys the plane in a wide circle watching for the Cuban boat. Within 15 minutes the two men and the raft are pulled on board the fishing vessel. A cheer goes up in the plane. Soon, the boat is heading for a port north of Key West. Immigration officers will be waiting. A man who escaped earlier this year with four other Cubans said in a phone interview, "The island was like a jail to me. To escape was the only thing left for me to do. "If I could get away, then I had a chance to know what freedom is. That's why I did it, to know what is freedom."