A San Francisco baby has developed what appears to be a mysterious and deadly disease that can destroy the body's immune system after he received a blood transfusion from a man who unknowingly had the disease at the time.

The alarming discovery by health researchers at the Centers for Disease Control was the first direct evidence linking a blood transfusion with Acquired Immune Deficiency Syndrome, or AIDS, a disease previously found only in some homosexuals, drug addicts, Haitians and hemophiliacs.

Since AIDS was identified in 1981, 788 cases have been reported, and 295 of the victims have died. Health researchers have been unable to discover what causes it or exactly how it is transmitted from one victim to another. New cases continue to pour into the CDC at the rate of about two a day. Eight cases have been reported in the Washington area.

AIDS destroys the human immune system, leaving its victims vulnerable to deadly infectious diseases, as well as a previously rare cancer called Kaposi's sarcoma and other malignancies.

"This is the first possible case of AIDS that can be linked with another case directly through a blood transfusion," said Dr. Harold Jaffe, one of the government's principal investigators of AIDS.

Dr. Edward Brandt, assistant secretary for health in the Department of Health and Human Services, yesterday called for an advisory committee to address the issues raised by the new findings.

A particularly sensitive problem is the development of guidelines for blood donations. The 48-year-old man who donated the blood used by the San Francisco baby who contracted the disease did not develop symptoms of AIDS until eight months after the transfusion, and is now dead. CDC officials said they did not know if he belonged to any of the known risk groups.

At the same time, a second CDC report to be released today, the Morbidity and Mortality Weekly Report, raises new concerns that the nation's 12,000 hemophiliac patients, who must receive blood products from many sources to survive, may risk developing AIDS.

The government health experts said that four new cases of AIDS and one suspected case have developed in hemophiliac patients receiving blood products. This brings the total number of hemophiliac cases of AIDS reported since last summer to seven definite, and one suspected. Five of the victims have died. The latest cases include two hemophiliac boys under the age of 10, who are still alive.

"The number of cases continues to increase and the illness may pose a significant risk for patients with hemophilia," the CDC said in notices to health departments across the country. Hemophilia is a relatively rare genetic disease that affects males. It keeps the blood from clotting properly and makes its victims more vulnerable to life-threatening hemorrhages.

In addition to the reported cases, sources said that CDC is aware of at least two other possible cases of AIDS-like illnesses in male and female patients who earlier received blood transfusions during surgery or medical treatment.

The government is tracking down about 20 suspicious cases, including four strongly documented ones, of AIDS-like illnesses in children in California, New Jersey and New York whose parents may have risk factors for the disease, medical sources said. Risk factors, in the language of medical investigators, mean that the parents might belong to one of the groups where the disease has been discovered.

The cases reported today strongly support the theory that the mysterious ailment is spread by an infectious agent, such as a virus, said Jaffe. But he and other government health officials cautioned that there is no evidence that AIDS is extremely contagious, although it may be spread through "intimate contact."

The initial outbreak among homosexuals, who now comprise about 75 percent of the total cases, suggested the disease was spread through sexual contact. The new reports add that it may also spread through contaminated blood products.

The hemophiliac victims with AIDS all received "factor 8 concentrate," which is a pooled blood product of extracts taken from at least 1,000 donors. The CDC said there was no evidence that a common lot of the product was involved. The cases are spread around the country.

The infant in San Francisco was born with a life-threatening condition called Rh disease, in which incompatibility in the parents' blood types can lead to destruction of blood cells in the developing fetus.

The boy, now 20 months old, received blood from 19 donors shortly after birth and began to show abnormalities as early as 4 months of age. By 14 months he showed unexplained immune system problems and had developed a serious bacterial infection commonly found in adult victims.

Because children sometimes develop different illnesses than adults do, and because there is no definitive test for AIDS, experts suspect that the child suffers from AIDS but are unable prove it. His illness is similiar to adult AIDS and does not appear to fit into known categories of rare immune system diseases affecting some children at birth.

The best evidence of a link with AIDS came when doctors discovered that one of the 19 transfusions involved blood platelets from the man who was in "apparently good health" at the time of donation in March, 1981 but became ill months later.

"One must assume that the [infectious] agent can be present in the blood of the donor before onset of significant illness and the incubation period of such illnesses can be relatively long," said the CDC report.

Another report is being prepared on the possible development of AIDS in other young children with unexplained immune system disorders. If such cases are confirmed, they would suggest another mode of transmission -- from mother to child, either during pregnancy or after birth, according to experts familiar with the cases under review.

The CDC is investigating about 20 possible cases involving children. Most of them are under the age of 2, and parents of many are thought to have known risk factors, including drug addiction or immigration from Haiti.

Jaffe and Dr. James Curran, head of the AIDS investigation, confirmed that CDC is investigating the children's cases. "It's of great concern," said Curran. "It's a very high priority to define this and determine whether it is a risk. If it's true, it exposes a whole new group to the problem."