The quest for an AIDS vaccine is progressing "very rapidly" and could result in an experimental vaccine by 1988, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said Sunday.

But even if scientists begin to test such a vaccine in 1988, Fauci said, it would take "at least a few more years after that before you get a vaccine that you can prove to be safe and efficacious." In total, it will probably be at least seven years, he said, before an AIDS vaccine could be on the market.

Fauci was one of several experts on acquired immune deficiency syndrome who addressed a symposium on the disease, jointly sponsored by the Association of American Physicians, the American Society for Clinical Investigaton and the American Federation for Clinical Research at the Sheraton-Washington Hotel.

Among their reports:

*New evidence that the AIDS virus, known as HTLV-3, may have been present in human beings in Africa as early as 1959. A retrospective study of 1,000 frozen blood samples taken in the mid- to late 1950s from residents of Zaire uncovered antibodies to HTLV-3 in some of the samples. "This suggests that the virus was there in 1959, but only in very small amounts," Dr. Myron Essex of the Harvard School of Public Health reported.

*Identification of a viral disease similar to an animal variety AIDS, known as STLV-3, among prostitutes in Dakar, Senegal. This new virus theoretically could be used in a vaccine against AIDS, because it might spur the body's immune system to recognize and combat HTLV-3 itself. "The recognition of a new member of this family of viruses being present only in healthy individuals suggests to us that this virus . . . may be a very productive tool for a vaccine against HTLV-3," Essex said.

*The discovery that AIDS infects not just a type of white blood cell known as the T4, but also other cells in the immune system, including B cells and monocytes. This suggests that the shutdown of the immune system "may not be due to loss of T4 cells, but to other problems," said Dr. Jay Levy of the Unversity of California at San Francisco.

*More evidence that AIDS may produce a wide variety of symptoms, including a little-recognized dementia. University of California's Levy reported on one patient, a computer operator who sought medical care because he was having trouble working. Six months later, Levy said, the man was dead of a dementia caused by the AIDS virus. Upon further investigation, researchers learned that the man's former lover had died two years before of a similar dementia.

The computer operator's present lover also developed the same neurological syndrome and died four months later. Tests showed that he, too, had AIDS, Levy said. Yet none of these men developed Kaposi's sarcoma or the opportunistic infections like pneumonia that claim most AIDS victims. Additional reports that AIDS seems difficult to spread -- except through sexual contact or blood products. The difficulty of catching AIDS is indicated by several studies, including one of 101 family members of AIDS patients who sometimes shared toothbrushes, razors, clothing, eating utensils and towels. Yet not "a single family member converted to having antibodies for the disease," said Dr. Merle Sande of San Francisco General Hospital.

A second study of 300 health care professionals showed similar findings. Presented at the meeting by J.L. Gerberding of San Francisco General Hospital, the study described 423 incidents of needle sticks and accidental splashes of bodily fluids from AIDS patients (including the case of one man who accidentally stuck himself 11 different times with needles from AIDS patients). Despite this exposure, none of the health care workers who did not otherwise fit into a risk group for AIDS developed antibodies against the disease.

In the search for an AIDS vaccine, the most encouraging advances come from two recent lines of investigation, Fauci said. Both involve proteins from the virus HTLV-3 (also called LAV), which causes AIDS.

HTLV-3 is surrounded by an envelope that is composed of proteins, and scientists have been able to identify, isolate and clone the viral gene that produces this envelope. They hope to use these proteins to mount an immune response by the body against the deadly virus.

At the National Cancer Institute, Dr. Peter Fischinger injected these envelope proteins into macaque monkeys, then gave the animals the HTLV-3 virus. The animals produced a "neutralizing antibody reponse," Fauci said, an indication that the monkey's immune system fought the virus.

Chimpanzees are more closely related to humans, and more sensitive to AIDS, than macaque monkeys are.

"The next step is to immunize chimpanzees with the same envelope and then to challenge them with the live HTLV-3 virus and see if they can protect themselves from infection," Fauci said. "We are in the process right now of doing that."

A second avenue in AIDS vaccine research involves combining the envelope gene with the vaccinia, or smallpox, virus. Conducted by Dr. Bernard Moss and Dr. Robert Gallo, both of the National Institutes of Health, this experiment with recombined virus has been effective in stimulating an immune response to AIDS in mice, Fauci said. "The next step is to see if a larger animal can be injected," he said.

The outlook for current AIDS victims, however, remains grim. "Although several patients have survived four years," Sande told the symposium, "even with our best efforts, we have not altered the mortality rate one bit." AIDS patients who contract one of the opportunistic infections, such as pneumocystis carinii pneumonia, survive an average six months, Sande said. Those who develop Kaposi's sarcoma live an average 17 months after the diagnosis is made, he said.

Almost three quarters of the victims are homosexual or bisexual men, and some 17 percent are intravenous drug users, who share needles and presumably some blood. But there are also 205 known cases of AIDS apparently transmitted from women to men, leading researchers to believe that "the disease can be spread heterosexually," Sande said.

Researchers continue to pursue new drugs that can help those with the disease. One of the most promising is AZT (3'-azido-3'-deoxythymidine), a drug developed by Burroughs Wellcome Co. in collaboration with federal researchers. AZT seems to work by interfering with the HTLV-3 virus's ability to multiply. Studies suggest that when the virus can no longer make copies of itself, no further infection can occur.

Whether these advances against AIDS will come in time to help current victims -- or even those with the pre-AIDS condition known as AIDS-related complex (ARC) -- is uncertain. An estimated 15,000 Americans have contracted the disease.

Preliminary studies of AZT at the National Cancer Institute and Duke University suggest that it "could be safely tolerated for a short term -- about six weeks," said Dr. Samuel Broder, head of clinical oncology and deputy clinical director at the National Cancer Institute. "We're still not sure what the best dose is, but armed with that information we feel that it is ethical to go ahead with this placebo-randomized clinical trail."

About 200 patients will participate in the multicenter study at NCI and other hospitals, including the University of Miami, Roosevelt/Cornell Hospital, Massachusetts General Hospital and the University of California at San Francisco.

The study "can be expected to go on for about six months," Broder said. "Carefully controlled trials are the best and fastest way to really address this problem. As soon as we find something that shows significant evidence of working, we will make every effort to make sure this drug is widely distributed."