Researchers from Harvard University and the National Cancer Institute for the first time have found AIDS virus in the saliva of persons who had close contact with known victims of the deadly immune system disease.

Dr. Robert Gallo, the NCI scientist who last spring announced that his laboratory had isolated a virus thought to be the primary cause of AIDS (acquired immune deficiency syndrome), confirmed yesterday that the organism had been isolated from the saliva of eight of 18 people who did not have the disease, but were known to be at risk of contracting it.

Gallo said that the individuals had had contact with AIDS patients, particularly homosexual men with the disease, or had some signs of a generalized illness that can sometimes precede AIDS.

He cautioned that it was impossible to tell from the data what role, if any, saliva might play in the transmission of AIDS, which has previously been isolated from blood samples. "We have to consider the possibility of salivary transmission which we had not considered before," said Gallo, but "I don't want to be alarmist." He called the findings "unexpected."

Researchers in the field have generally stressed that AIDS seems to be transmitted through intimate contact, largely through sexual contact with bodily fluids, or transmitted through blood products.

Gallo said he believes that even if saliva plays a role, it was highly unlikely that the virus, known as Human T-Cell Leukemia Virus, or HTLV-III, would be transmitted through casual contact, "certainly not by a peck or by a glass."

But, he said, "heavy kissing is a theoretical possibility" and should be followed up in research studies of AIDS. "It is extremely important to look case-by-case to see if it can occur this way."

His new study, which he said will be reported in the October issue of Science magazine, was done in collaboration with Harvard University clinician Dr. Jerome Groopman, who provided the patient samples for analysis.

Gallo said that while the saliva samples from some individuals who had contact with AIDS patients contained the virus, the virus was not found in the saliva of AIDS patients who were tested, but only in their blood. He said that this may be because the virus has already done its damage in the AIDS victim and little remains in the body.

Gallo indicated yesterday that his laboratory had also proven that the virus was present, as expected, in semen.