Acquired Immune Deficiency Syndrome, or AIDS, an immune system disease now striking in epidemic proportions in the United States, may also occur in equatorial Africa, according to three new medical reports.

Calling the connection "striking," a research team sponsored by the French Ministry of Health suggests that "equatorial Africa is an endemic zone for the supposed infectious agent s of this illness" and that it may well not be as new as suspected.

In the current issue of the British journal Lancet, the 14-member Study Group on the Epidemiology of AIDS in France reports on 29 suspected cases. Ten of the victims had traveled to Africa in the five years before getting the disease.

Two other recent letters from French and Belgian doctors in Lancet and the New England Journal of Medicine also describe six cases of the deadly disease in previously healthy Africans.

The reports are likely to fuel debate about the mysterious origin of AIDS, whose cause is still unknown. It attacks the body's natural defense system, making its victims vulnerable to life-threatening cancers and infectious diseases.

Most researchers believe that an infectious agent, perhaps a virus, is responsible, but there is little agreement among American experts about whether it is a new organism or a old germ that was transported here recently.

AIDS was first reported in the United States in June, 1981, among homosexual men and has since been found in drug addicts, Haitians here and in their native country, hemophiliacs, other recipients of blood transfusions and children. Followup studies suggested that the earliest known AIDS cases, in 1978, had appeared in New York and Haiti about the same time.

The federal Centers for Disease Control reports 1,279 U.S. cases, with 485 deaths, as of March 31. Seventy-six foreign cases also have been reported to CDC, but until the new reports, none had come from Africa, officials say.

It is well-known that Kaposi's sarcoma, an unusual cancer that afflicts AIDS patients, has long been common in equatorial Africa, striking older people and children in a milder form.

But the new reports suggest that both AIDS-like cancers and infections are found in recent immigrants from Zaire and Chad as well as travelers to several African countries. Of the 29 French cases, four of five heterosexual patients with life-threatening infections had never been to the United States or Haiti, but had lived in equatorial Africa, doctors there said. Nine of the cases were diagnosed before June, 1981.

Dr. James Curran, head of the CDC task force on AIDS, yesterday called the new information "valuable and important work" which could trigger more interest in exploring the African connection for clues to the cause of AIDS. But, he emphasized, the task force has not had a chance to review the cases.