MIAMI, Florida -- The Clinton administration, reversing a 30-year-old policy in the face of a surge of refugees fleeing Cuba by boat and raft, has announced that those who reach the United States will be held in detention camps rather than being permitted to settle in Florida or other parts of the country.


The policy change, unveiled late Thursday by Attorney General Janet Reno, came after an emergency appeal by the Florida Governor Lawton Chiles and intelligence reports showing that thousands of Cubans are massing to set sail for the United States.


Reno said the administration wanted to "be sure we did everything we could" to discourage Cubans from making the voyage before the refugee situation got out of hand.


The administration is trying to stave off a repeat of the Mariel boatlift of 1980, during which some 125,000 Cubans streamed into South Florida over a five-month period.


The detention policy was one of several under consideration since the number of refugees began swelling this week. The Coast Guard said its vessels picked up 369 Cubans in the South Florida straits Thursday, after a record-breaking 537 Wednesday. Those figures are up from a rate of about 300 refugees a day last weekend.


Reno gave no indication how the administration plans to detain refugees picked up at sea but officials suggested that some could be housed at federal installations in Florida.


The administration already has made plans to open tent-cities to hold some 8,000 refugees at Homestead and Key West to serve as screening centers.


It was not immediately clear Thursday whether refugees would be afforded formal hearings to determine whether they should be allowed to settle in the United States. Under current law, U.S. officials do not have to accept Cuban refugees, but once they allow them to settle in the United States, the Cubans are granted immigrant status.


And key administration policy-makers said the White House is also considering asking other Caribbean countries to accept some Cuban refugees temporarily, as Jamaica did in the case of Haitian boat people.


The administration is debating other options, ranging from increasing the number of Coast Guard vessels assigned to pick up Cubans to tightening pressure on Cuba to stop encouraging dissidents to leave.


The White House also is expected to announce soon a plan to make it easier for Cuban nationals to apply for standard immigration visas at the U.S. Interests Section in Havana, which functions as an unofficial U.S. embassy.


The action Thursday amounts to a major policy reversal for the Administration, which until now has maintained that it is obliged under the 1966 Cuban Adjustment Act to allow all Cuban refugees to settle in the United States.


Actually, the law permits the Immigration and Naturalization Service to refuse entry to Cubans who do not qualify for immigration status. But since Cuba has declined to take them back, those people have no place to go.


Reno's announcement came after an emergency meeting of Clinton's top national security advisers earlier Thursday, in which policy-makers reviewed the refugee situation and possible options for dealing with it. Although Clinton did not attend the meeting, officials said he was briefed on it later and decided to go ahead with the detention plan.


Chiles said after the announcement he was delighted with the administration's new move. "We do need to send a very clear message to Cuba," he said. "This keeps Castro from being able to call the shots."