BY NANCY SAN MARTIN

  Speaking in Miami on Monday, the top U.S. diplomat in Cuba blamed Fidel Castro's government for a growing atmosphere of desperation inside the country
  and suggested that it could generate another mass exodus to Florida.

  ''Most of Cuba's exhausted citizens appear to simply be waiting for change with a mixture of hope and trepidation,'' James Cason, chief of the U.S. Interests
  Section in Havana, said at a luncheon at the Univeristy of Miami's Institute for Cuban and Cuban American Studies.

  ''Unfortunately, as a neighbor, Cuba's problems can become our problems, too,'' Cason said. "Apart from the moral imperative driving our support for
  democracy in Cuba, we have a strategic interest as well. The continued disintegration of Cuban society generates instability throughout the region and
  creates the threat of a mass migration to the United States.''

  Cason said tension has increased on the island since the arrests of some 80 dissidents across the island. A number of activists were sentenced on Monday
  to terms of 15 to 25 years in prison on charges of collaborating with U.S. diplomats to undermine the socialist state.

  ''A month ago I would have started this speech drawing attention to the fact that the Cuban people had managed to preserve their fundamental dignity in
  the face of more than four decades of repressive rule. Today, I must say that dignity is being stretched very thin,'' Cason said. "The Castro regime has
  shown that it is willing to risk even the ire of the international community to maintain its central role.''

  Cason also said he did not believe three recent hijackings -- two airplanes and a ferry -- were ''orchestrated'' by the government, but rather the result of
  desperate acts by individuals unaware that U.S. policy does not welcome hijackers.