A federal law that restricts the number of foreign medical school graduates who can train in U.S. hospitals may "clobber" many smaller hospitals that depend on the graduates to fill many of their resident physician posts, the director of Harvard's main teaching hospital said yesterday.

Dr. Charles A. Sanders, director of Massachusetts General Hospital, said Harvard teaching hospitals will have no trouble attracting enough American med school graduates to fill their residencies.

But Sanders said that Health Manpower Act, which takes effect July 1, 1977, will end Mass General's tradition of training foreign physicians who later return to their countries to spread U.S. medical knowledge.

Many countries whose physicians get advanced training in the U.S. hospitals will have to establish their own facilities to provide this training, unless future administrative clarification of the act gives foreign med students freer access to U.S. hospitals, Sanders said.

About 14,000 students graduate from U.S. med schools each year, but more than 14,000 residencies open up in a given year. Graduates of foreign med schools now make the difference, Sanders said.

Sanders said the duplication of teaching facilities would slow the dissemination of medical knowledge and cut down the total knowledge shared between countries.

The law says that foreign med school graduates can only immigrate for residencies if they have passed both parts of the National Medical Board Examination, which is given only in the U.S., or an equivalent.

The definition of "equivalent," to be set by the Department of HEW will determine how restrictive the law will be.

If it is difficult for foreign students to gain access to an equivalent exam, the law will favor the "priviliged few" who can come to the U.S. on a visitor's pass to take the National Medical Board Exam, Sanders said.

The bill makes no allowances for foreign physicians-in-training who plan to return to their native countries after finishing their U.S. residencies, Sanders said.

He added that in his opinion the regulations should distinguish those students from students who use their U.S. education as a means to immigration.

Fifteen per cent of Mass General's 600 residents and fellows training in a sub-specialty are graduates of foreign schools.