The recent report that a 15-year-old St. Louis boy who died in 1969 apparently had AIDS, more than 10 years before the first U.S. cases were reported, does not change current theories about when and how the epidemic originated, researchers said.

"I think it's absolutely predictable" that such a case would be found eventually, said Dr. Robert Gallo of the National Cancer Institute, one of the discoverers of the AIDS virus. "If AIDS was recorded in epidemic proportions in 1981 on both coasts of America, and if the latency period is many years, then there had to be episodic infections in Americans several years before," he added.

An article in Sunday's Chicago Tribune described the puzzling case of Robert R., a teen-ager who died in a St. Louis hospital a decade before the first known U.S. AIDS patient became ill in New York City. During his two-year illness, Robert R.'s symptoms included fevers, weight loss, unusual infections and severe swelling of his lower body. An autopsy revealed Kaposi's sarcoma, a cancer that was rare at that time but that is frequently found in AIDS patients.

Stored samples of Robert R.'s blood have now tested positive on two different tests for infection with the AIDS virus, including one that detects antibodies -- chemicals manufactured by the immune system against viral proteins -- and another that picks up a protein called p24 from the virus, said Dr. Robert Garry, associate professor of microbiology at Tulane University Medical School.

But Garry agreed with Gallo's assessment that Robert R.'s case does not challenge the prevalent view that infection with the AIDS virus was extremely rare in the United States before the late 1970s.

"I don't think it changes anything," Garry said. "Till other cases are uncovered, if they ever will be, all we have is one case. But it's a case."

Although the test results and the diseases suffered by Robert R. fit the diagnostic criteria for AIDS, how he might have become infected with the virus is a mystery. When he was hospitalized at 14, he told his doctors he had had sexual intercourse with a neighborhood girl, said Memory Elvin-Lewis, a professor of microbiology at Washington University Dental School who was involved with the case.

He was severely infected with chlamydia, a sexually transmitted disease, Elvin-Lewis said. Dr. Marlys Hearst Witte, a University of Arizona surgeon who treated him in St. Louis, told the Chicago Tribune that he also had swollen genitals and severe anal inflammation, evidence of possible homosexuality, and suggested he could have been a male prostitute.

But AIDS was unknown at the time, and "the question of homosexuality was not even asked of the patient," said Dr. William L. Drake, Jr., an associate clinical professor of pathology at St. Louis University Medical School, who performed the autopsy. Nor was Robert R. asked about drug abuse, Drake said, adding, "in the several months that he was a patient I'm sure it would have come to light."

The earliest U.S. cases of the disease that became known in 1981 as AIDS were seen in New York and California hospitals in 1979. Gallo said he believes the virus originated in African monkeys and may have infected humans sporadically for centuries. He said social changes in Africa and increased migration into cities, not changes in the virus's biology, probably accounted for the epidemic.

"These are very ancient viruses," he said. "They're not new. They didn't come into being just yesterday."

The earliest African blood samples showing evidence of human infection with the AIDS virus date from 1959, Gallo said. He said Belgian researchers reported African cases in the 1960s that, in retrospect, were probably AIDS. Single, unexplained cases of Pneumocystis carinii pneumonia, an infection later found to be common in AIDS patients, occurred in England and the United States as early as 1959. And a few unexplained cases of Kaposi's sarcoma were reported during the 1960s.

Robert R. reportedly never traveled outside the Midwest, but Gallo said that he could been infected by someone who acquired the virus elsewhere.

Gallo said researchers have tested large numbers of U.S. blood samples from the early 1970s and have not found any that tested positive for infection with the AIDS virus, he but added that he was "not in the least" surprised by news of the St. Louis case.

"I don't think it changes a single bit of thinking about this virus," he said.