"There are drafts and people are trying to think about what is going to happen should there be a change in the political situation in Cuba," said White House spokesman Tony Snow.

"If there is a change, a dramatic change in the political situation in Cuba, there may be adjustments in US policy," Snow told reporters in Crawford, Texas, near President George W. Bush's ranch.

After four-and-a-half decades hoping for the demise of Castro, who turns 80 on Sunday, the United States at first reacted cautiously to his surprise transfer of power to brother Raul, after surgery, announced on July 31.

Washington promised to stand by political activists who want to spark political change on the island, but called on Cubans to stay at home, worried that political tumult could spark mass migration to the coast of Florida.

The State Department has simultaneously warned that the transfer to authority to Raul Castro, 75, must not become permanent, saying that would just mean one dictator swapped for another.

"The Cuban people need to decide the future of their country," Bush said on Monday, in remarks seen as partly directed at the fiercely political Cuban exile community in the United States.

While it wants Cuba to track toward democracy, Washington, beset with a bevy of foreign policy crises, could do without a hard political landing on the island and a resultant humanitarian crisis.

"A wave of refugees towards Florida would not be good politics," Ian Vasquez, of the Cato Institute in Washington told AFP.

"Nobody wants destabilisation in Cuba, especially president Bush because he's get already too many things on his agenda on foreign policy."

The scale of any mass exodus could be immense -- in the last immigration crisis in 1994, a staggering 35,000 people crossed the Straits of Florida from Cuba, 90 miles (150 kilometres) off the US coast.

On that occasion, Cuban authorities did nothing to stem the flow of people leaving the country; analysts fear an even worse situation could arise if order breaks down in a post-Castro Cuba.

In recent days, the White House has been assessing how to prevent any such tsunami of refugees, the New York Times reported Tuesday.

Washington is likely to stick with its quota of 22,000 visas given to Cubans every year -- and will give priority to those who already have family members living in exile in Washington, the paper said.

Such a move is designed to strictly control the flow of legal immigrants, to ensure numbers remain manageable.

On the political front, the United States is readying financial aid to help unshackle the Cuban economy after decades of communist control, and will be ready to help bankroll any move toward democracy.

"The United States ... is planning to provide substantial support to help them rebuild their shattered economy," Caleb McCarry, Bush's Cuba transition coordinator, said on Fox News.

Washington would also "help provide specific support for getting to free and fair elections and also to provide specific support, as I said, to help them address the long humanitarian needs," he added.

Snow stressed that so far, there had been no change of longstanding Cuba policy, which stressed opposition to Castro, support for democracy on the island, and includes a trade embargo.

"I daresay if there were changes in Cuba and we had not thought ahead, the question would be, 'why didn't you think about changes that were taking place,'" he said.

Bush, operating in a potentially dicey congressional election year for his Republican Party must walk a fine line, as Cuban exiles form a crucial voting block in Florida -- the state that sent him to the White House after a disputed election in 2000.

His administration is aware Cuban exiles may press hard to tip the balance in Cuba and could spark political instability there -- especially as many want redress for assets seized by the communist government.

Once Cubans form a government, "then Cuban-Americans can take an interest in that country and redress the issues of property confiscation," Bush said in Texas on Monday.

The United States has called on its allies to help press for a democratic transition in Cuba.

Secretary of State Condoleezza Rice on Sunday however denied Washington was trying to stoke a crisis in Cuba.

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