HAVANA -- American medical students in Cuba have rushed back to the United States, missing their final exams, over fears that U.S. authorities will jail them, fine them thousands of dollars, or revoke their citizenship for studying medicine on the island.

New Bush administration measures that took effect June 30 severely restrict Americans' presence on the island.

The Office of Foreign Assets Control, an arm of the Treasury Department, issued a letter June 25 saying the students could stay until Aug. 1. But many students didn't get the word in time.

"The majority of the students have left," said one student, Naketa Thomas, 26, of New York.

James Cason, the top U.S. diplomat in Cuba, said he wasn't aware the American students were cutting their educations short.

"It wasn't our intention," he said. "We'll have to get word to them somehow."

Before the frenzied departures there were nearly 80 American medical students in the country. Few remain, perhaps half a dozen, American students say.

Inspiration for the program goes back to 1999, when U.S. Rep. Benny Thompson, D-Miss., told Cuban President Fidel Castro that there were few doctors in his district in the Mississippi Delta.

In September 2000, Castro told a crowd at Riverside Church in New York City that he would give scholarships to underprivileged Americans who couldn't afford medical school. The Cuban government would pay the costs of the six-year program, Castro said. The only catch: After the students graduated, they would have to practice medicine - at least for a time - in their own needy neighborhoods.

Hundreds of Americans applied for the program. At least a dozen of those who initially arrived dropped out because they couldn't stand the conditions at Havana's Latin America School for Medical Sciences.

Eight to 14 students are packed into each dorm room, sleeping in bunk beds. The food isn't always edible. There's no air conditioning and the toilets have no seats, students say.

"Conditions are really basic," Thomas said. "The water is cut off at 11 p.m. Some students don't like that. ... I say: `We're in Cuba. Fill a bucket with water and take your bath whenever you want.' "

Thomas said she doesn't mind the conditions. She's grateful for the chance to get a medical degree and not pay the $100,000 to $200,000 it can cost at home.

"Now they're telling us to leave. What are we supposed to do?" she asked. "I think it's unfair. We're all here because we could not pay the tuition they charge in the United States."

The Rev. Lucius Walker Jr., executive director of the Interreligious Foundation for Community Organizing in New York, which has recruited students for the program, said: "It's not a good situation. I'd like the U.S. government to come to its senses and exempt these students from the restrictions. They're not terrorists. They're not agents. They're simple ordinary kids from humble backgrounds."

The U.S. measures to restrict travel to Cuba are "devastating, cruel and damaging," he said. "These regulations are hurting these kids. If the intent is to punish Cuba or somehow force Cuba to do whatever the U.S. wants it to do, it's not working."

Bush administration officials say they are restricting travel to Cuba to cut off the flow of hard currency to the island.