The "wet foot, dry foot" policy, which does not apply to any other immigrant group, is being blamed by critics for at least 39 deaths this year in the Florida Straits and is testing the resolve of the Coast Guard, which the critics say has become too aggressive in enforcing the restrictions.
In offering a permanent escape to Cubans who make it here, they say, the policy encourages them to risk their lives.
Coast Guard data show that as of Friday, 2,683 Cubans had been intercepted at sea this year, nearly double the number for all of 2004. And while the high season for migrant crossings, when the sailing tends to be smoothest, is already past, scores have kept trying the journey despite the perils.
Some of the migrants, hoping to avoid confrontations with Coast Guard patrols, are taking unusual routes, to the United States Virgin Islands and the Gulf Coast of Florida. A fast-growing number - including 6,744 counted by Customs and Border Patrol in the fiscal year that ended in September - are entering the United States by slipping across the Mexican border, often after sailing some 500 miles to Honduras from Cuba.
The State Department says the new wave of migrants is a result of increasingly repressive policies in Cuba, the island's crumbling economy and Mr. Castro's refusal to let more Cubans sign up for a lottery under which the United States is supposed to grant 20,000 visas a year.
But some Cuban-Americans in South Florida say that new limits on their visits and on the money they can send to relatives on the island, imposed by the Bush administration last year, have led to greater desperation among many Cubans.
Ever more aggressive smuggling has also played a role. Far more Cubans are making it to American shores, including, for example, 14 migrants discovered near a parking lot on Marco Island, Fla., a few days after Thanksgiving. About 2,530 completed the journey to South Florida in the last fiscal year, compared with 954 the year before, according to the Border Patrol.
"The message to Cuban families is that if you don't want to wait in line, your relatives in Miami can pay $8,000 and you've got a good chance to make it here," said Philip Peters, a Cuba analyst at the Lexington Institute, a research group in Washington. "It really is a glaring exception in the whole homeland security policy."
One incident this fall perhaps best encapsulated the growing resolve of Cubans to slip into this country and of the federal government to keep them out.
Florida television audiences watched as government agents struggled to keep 10 migrants in a homemade metal vessel from reaching the beach just north of Miami after a Customs and Border Protection boat bumped it hard enough to spill some of the migrants overboard. Coast Guard boats had also sprayed the vessel with a hose and tried stalling its engine with a rope during a prolonged showdown with the migrants, all men.
"We are needlessly putting innocent lives at risk," said Cheryl Little, executive director of the Florida Immigrant Advocacy Center, which helps Cuban and other migrants pursue asylum claims. "Our Coast Guard is being put in the untenable position of endangering lives in order to keep people from reaching our shores."
Luis Diaz, a spokesman for the Coast Guard in Miami, said that the agency's tactics had not become more aggressive but that unlike in the past, it was working closely with agencies like Customs and Border Protection since becoming part of the Department of Homeland Security in 2002.
"We are working better and smarter with our partners," Mr. Diaz said. "Before we were in Homeland Security we had different radios, different frequencies, and now we are working together behind the same equipment."
The number of Cubans being intercepted is by far the highest since 1994, when 37,000 took to the Florida Straits after Mr. Castro announced that his government would no longer stop boats or rafts leaving the island. It was a hostile move against the United States and a way for Mr. Castro to divert attention from his domestic problems and quell an uprising against him on the island, similar to when he let 125,000 Cubans leave in the Mariel boatlift of 1980.
The 1994 exodus led the United States and Cuba to agree on the wet foot, dry foot policy in 1995, ending this country's longtime practice of admitting all Cuban migrants as refugees.
Many of the Cuban migrants are paying thousands of dollars, often provided by relatives here, to smugglers who whisk them across the Florida Straits on speedboats, several of which capsized this year. In one such case, a 6-year-old boy drowned after the boat he was riding in fled a Coast Guard cutter in October. In another, an Antiguan merchant ship rescued three migrants who said that 31 others had drowned when their 28-foot boat overturned in August.
Others are still trying the dangerous trip on rafts or vessels of their own making, some of which are spotted by fishing boats and cruise ships that report them to the Coast Guard. Those intercepted at sea can get preliminary asylum interviews aboard Coast Guard cutters, but only a few are deemed eligible for second interviews. They get sent to the United States Naval Station in Guantánamo Bay, Cuba.
If found to have a credible fear of persecution, they still cannot come to the United States and instead are resettled in other countries like Spain and Australia.
Only about 2.5 percent of Cubans intercepted at sea in the last fiscal year were taken to Guantánamo and considered for asylum, according to the Department of Homeland Security. Even of those, most were eventually returned to Cuba.
Even as the number of Cuban migrants balloons and President Bush proposes new laws to curb illegal immigration, there is no plan to re-examine the wet foot, dry foot policy, said Janelle Hironimus, a State Department spokeswoman. She said Mr. Castro's policies were behind the increase in migration efforts.
"Castro's repression of his own people and refusal to allow the basic freedoms enjoyed by people everywhere have led to a mass migration by the Cuban people," Ms. Hironimus said.
But some Cuban-Americans in South Florida say Mr. Bush's refusal to make exceptions to the current policy is evidence that he is deserting the anti-Castro cause.
They were particularly angered by a case last month in which Jorge Ernesto Leyva, who had recently emigrated from Cuba, drove a rented speedboat to Havana from Key West, packed the 27-foot boat with 37 relatives and tried to return here clandestinely. But the sea turned violent and as the passengers were bailing water, a Coast Guard helicopter spotted the boat and directed a cutter to intercept it.
The Coast Guard crew had transferred only about half of the migrants to its cutter when the speedboat capsized, trapping two grandmothers and a 9-year-old girl underneath. The girl's mother dived under the boat to rescue the girl, but nobody saved the two women - even though Mr. Leyva and others on his boat said they begged the Coast Guard crew to do so.
Mr. Diaz, the Coast Guard spokesman, said rescue diving was not part of the Coast Guard's standard procedures.
"People ask us, 'Go underneath the hull,' " he said. "Well, we don't carry divers. If our personnel jumped in the water, then no one is going to be manning the ship. We have just enough persons to run a vessel. We don't have extra bodies to do things some of these relatives want us to do."
Mr. Leyva and a teenager on the boat were brought to Florida because they had been admitted previously. The others asked permission to attend the funerals of the drowned women, who were 74 and 60. But the Department of Homeland Security denied their request and returned them to Cuba.
"We are concerned about the policy and the effect it has on the way the Coast Guard does its business," said Matthew Archambeault, a lawyer for Mr. Leyva and his family. "We do feel they sacrifice safety to keep people away from dry land."
Terry Aguayo contributed reporting from Miami for this article.