By KAREN W. ARENSON
 
The United States government stopped a group of about 70 American medical school professors, doctors and other scientists from attending an international symposium on coma and death in Cuba this week, several doctors said yesterday.

Scientists say the prohibition against the trip, with only a few days' notice, is the latest step by the Bush administration to limit their work with people in countries like Cuba that are seen as hostile to the United States.

"They're trying to punish these countries they've identified as evil," said Stuart J. Youngner, a professor at Case Western Reserve University who helped organize the conference. "But the end result of this is an infringement on academic freedom, our freedom as citizens to travel and also damaging to science in the United States and around the world."

Alan I. Leshner, chief executive of the American Association for the Advancement of Science, said his group was alarmed by the government's opposition to the Cuba trip, as well as by its recent ban on the editing of papers submitted by people in countries facing sanctions and by restrictions on study by foreign students in the United States. "Their actions to restrict open communication in science work against our national interest," he said.

The opposition to the trip came through the Treasury Department's Office of Foreign Assets Control, which oversees travel to Cuba and notified the agent licensed by the department to handle travel there. A spokeswoman for the Treasury Department declined to comment.

The Cuba conference was the Fourth International Symposium on Coma and Death, which starts today. About 200 scientists from around the world were to participate.

Dr. E. Roy John, a professor at New York University's School of Medicine and director of the Brain Research Laboratories there, who was scheduled to deliver two papers, said he had been particularly interested in sessions on bringing people out of comas through more active treatment.

Dr. John and other researchers said that in areas like molecular biology and mathematics, Cuba was "world class."

The scientists planning to attend the conference thought that their trip was permitted under government regulations that let professionals attend international meetings sponsored by international organizations in Cuba, and for research and other educational purposes.

But in late February, some scientists received letters from the Treasury Department warning that they risked criminal or civil penalties if they broke the embargo against Cuba by attending the conference.

Some doctors sought help from their senators and Congressional representatives, and on Thursday thought that they would be able to go.

But Bob Guild, program director at Marazul Charters Inc., who was handling travel arrangements, said the Treasury Department told him late Thursday that the State Department had rejected the trip because it had been initiated by a Cuban.

Mr. Guild said there had been no problems with Americans attending the three preceding conferences in Cuba, which were handled the same way. He said that plans for Americans to attend several other Cuban conferences have either been called off or are also in jeopardy.