Two American scientists and a French immunologist won the 1980 Nobel Prize in medicine yesterday for their landmark discoveries on how genetic makeup determines the body's response to infection and to the development of cancer.

The work of the three men has helped make transplant operations, such as kidney transplants, safer and has contributed to explaining why some cancer cells are eliminated from the body while others remain to establish one of the 105 known types of cancer.

The Royal Caroline Institute of Medicine named Baruj Benacerraf, 59, a Venezuelan-born American citizen who is chairman of the Department of Pathology at Harvard Medical School and president of the Sidney Faber Cancer Institute in Boston; George Snell,76, senior staff scientist emeritus of the Jackson Laboratory in Bar Harbor, Maine; and Jean Dausset, 63, of the immunological laboratory of St. Louis Hospital of Paris University.

The prestigious award, which this year totals $211,000 to be shared among the three recipients, cited their work on "genetically determined structures on the cell surface that regulates immunological reactions."

The three working separately but aware of each other's research, studied how the body's own immunological system -- the same system that prevents one from catching a cold -- might have a role in whether the body fights or yields to cancer-causing elements or infection, or accepts or rejects foreign matter. Individuals' immunological defenses are genetically determined as part of their inheritance from their parents.

Like much Nobel-winning research, the body of their work represents a signigicant advance at the basic level, on which others at the applied level of science can build, a spokeswoman at the National Cancer Institute said yesterday. Another source at the National Institutes of Health noted that if people genetically more susceptible to cancer could be pinpointed, they could be watched particularly closely for the earliest development of the disease -- the stage at which any cancer is most curable.

Dausset, reached in Paris by the Associated Press, said that he, Benacerraf and Snell were "excellent friends and, even though we didn't work together, we have been exchanging the results of our experiments for a long time." He told the AP that he had visited the others' laboratories in this country and that they had visited his institution in France.

The Nobel citation said that Snell's discoveries led to the development of transplantation immunology. He helped establish the rules of transplantability, the institute said.

The citation said Dausset's work opened the way to research on the rules of transplantation in man and made it possible to type both the donor and recipient in kidney transplants, thereby improving the success rate of kidney transfers.

Benacerraf's work, the institute said, helped explain why some individuals are able to mobilize strong immunological responses to infections while others are not.

It said the work of the three also helped in investigations of disputed paternity and in anthropological and evolutionary studies.

All three studied antigens, or protein-carbohydrate complexes that are found on every cell membrane in the body. Formation of these antigens on the "skin" of a cell are regulated by the genes found within the cell.

Benacerraf, who moved to the United States from France in 1940 and became a citizen in 1943, received degrees from Columbia University and the Medical College of Virginia. He served in the Army, did research at Columbia and for six years at Broussais Hospital in Paris, then joined the New York University School of Medicine in 1956. He joined Harvard in 1970.

In Boston yesterday, he said the prize was an endorsement of the American system of research. "This only happens in the United States because we here have supported research and have encouraged young people to go into this kind of endeavor," he said. He added that the award had taken him by surprise and that he was "overwhelmed" with pleasure.

Snell, who was born in Bradford, Mass., is a zoologist. He learned of his award in a conference call from his three sons yesterday and called it "the most overwhelming thing that can happen to you." He was educated at Dartmouth and Harvard and taught for several years before joining the Jackson Laboratory, where he spent nearly 40 years before retiring.His many honors include the Gregor Mendel Medal from the Czechoslovak Academy of Sciences in 1967.

Snell said that the major practical application of his work is in kidney transplants and other organ transfers. "It's also shed a great deal of light on immunology -- infectious diseases -- and some that aren't infectious, such as multiple sclerosis.

"The work stretched over a long period of time," he noted. "It's not a sudden burst of light, but something you plug away at over quite a long period."

Of the four Nobel recipients named so far this year, three are Americans. The United States has dominated the Nobel annals, particularly in science categories, and more strongly than ever in the last five years.

The Royal Caroline Institute worked for a year sifting out the recipients from more than 100 candidates.