An American medical delegation yesterday said it had found "unmistakable physical evidence of torture, starvation and malnutrition" and "a complete breakdown in medical care" in a visit to El Salvador sponsored by eight health groups including the American Public Health Association.

The seven-member delegation urged President Reagan not to recertify that the country was making progress in respecting human rights.

The delegation returned Wednesday after talks with Salvadoran exiles in Mexico City, followed by four "20-hour workdays," they said, in the San Salvador area, touring hospitals, clinics, prisons and a refugee camp.

They said that exiles, prisoners and Catholic and Lutheran workers had told them that much of what they saw was the result of repression by the Salvadoran army. Defenders of El Salvador's government say Salvadoran guerrillas are equally responsible for murder and abuses.

"I was totally overwhelmed and shocked, as a physician, at all we saw," said Dr. John Stanbury, emeritus professor of nutrition and experimental medicine at the Massachusetts Institute of Technology.

"There is a terrible and conspicuous lack of humanitarian services from the international community, including the United States," he said, despite efforts by Catholic and Lutheran groups and the U.S. Agency for International Development.

The delegates urged international and American health and food aid.

The nation is suffering "a catastrophic health emergency," and drugs and anesthetics are scarce or nonexistent in San Salvador hospitals, according to Dr. Carola Eisenberg, dean of students at Harvard Medical School.

Garbage fills streets, said Ann Hargreaves, Boston's assistant deputy commissioner of health and hospitals, and amoebic dysentery, typhoid, tetanus and malaria are on the increase.

In meetings with nearly 50 prisoners in the capital's two main prisons, delegates said, they saw physical evidence of "obvious torture"--beatings, acid burns and sexual abuse, which prisoners said occurred at army detention camps.

At a refugee camp, the group found 1,500 war-zone refugees, 500 of whom had arrived in the last two weeks.

"I've been in and out of Latin America and Africa for 30 years," Stanbury said, "and I've never seen people in such appalling physical condition except in hospitals in chronic famine areas."

Stanbury and Dr. David Halperin, an Augusta, Maine, surgeon, examined 80 children and saw "protruding abdomens, discolored hair, skin diseases, lice, scabies, running sores and running noses."

The $12,000 trip was paid for by the Committee for Health Rights in El Salvador, a New York group that relies on donations; the American Medical Students Association, and the Committee of Interns and Residents. Several members of the delegation spoke fluent Spanish.