In a major advance toward understanding the cause of cancer, scientists have found that an interaction between a virus and a gene is responsible for many forms of the disease in animals, and probably in humans as well.

A key discovery is that viruses somehow can change the functioning of a gene that is essential to all higher animals, Dr. Wallace P. Rowe of the National Institutes of Health said. Once changed, the gene turns normal, controlled cells into the malignant cells of cancer.

Studies of the virus-gene interaction are boing carried on intensively in several laboratories.

About 10 genes capable of causing cancer have been identified in various animals, Rowe said. The one under the most intense study is the MAC gene, so named after a virus in which it was found. The gene is found in essentially unchanged form in species ranging from fruit flies to humans.

There are two ways a virus can make the MAC gene capable of turning a normal cell cancerous, Rowe said. One is for the virus to pick up the gene from a normal cell. When the virus infects another cell, the presence of the MAC gene can turn that cell malignant.

A second way, discovered only inthe past few months, is for a virus to incorporate part of its genetic material near the MAC gene in the nucleus of an infected cell. Cells that have turned cancerous have been found to have part of the virus' genetic material in a specific spot near the MAC gene.

Either way, a gene that apparently plays an important regulatory role in the normal cell goes wrong, probably because the virus interferes with the mechanisms that regulate the gene.

Almost all teh research thus far has been done in animals. The studies of the way that the virus integrates itself near the MAC gene have used awell-known chicken cancer virus, the Rous sarcoma virus. But one laboratory has found evidence of MAC gene activity in some patients with a rare form of human leukemia.

The gene-virus studies will have no immediate effect on the treatment or prevention of cancer, Rowe said. But the impact of the studies will be great because of the new light they will shed on the process by which cells turn cancerous.

Researchers studying viruses in cancer have always looked for signs of complete viruses in cancer cells, Rowe said. The new discovery indicates that they should look instead for the small part of the virus gene that takes up residence near the MAC gene.