By MIRTA OJITO

Thousands of Cuban doctors have defected in the 48 years since the government launched its first international aid mission. But the pace has accelerated in the past five or six years, experts say, as the number of doctors abroad increased and, particularly in the past two years, as the United States made it easier than ever for Cuban medical personnel to obtain U.S. visas through the Cuban Medical Parole Program.

Officials at U.S. Citizenship and Immigration Services would not release the number of doctors who have obtained visas through the parole program. Chris Rhatigan, an immigration service spokeswoman, said that such information could ``jeopardize the program.''

Calling the program ''a tremendous success,'' Ana Carbonell, chief of staff for U.S. Rep. Lincoln Diaz-Balart, R-Miami, said that more than 1,000, ''perhaps closer to 2,000,'' doctors have already obtained U.S. visas.

And Julio Cesar Alfonso, president of Solidaridad sin Fronteras, a Miami-based organization of Cuban doctors, estimates that in the past five years, 6,000 doctors have defected. About 5,000 of them are in the United States and 2,600 of those have joined Solidaridad, he added. The rest are scattered all over the world.