The federal Centers for Disease Control has eliminated a separate listing of Haitians from its weekly report of patient groups with a known risk of incurring acquired immune deficiency syndrome (AIDS).

The action comes more than 2 1/2 years after Haitian immigrants were singled out as a risk group, an action that led to complaints of discrimination against Haitians in this country and a reported drop in tourism in Haiti.

While other risk groups have been linked with sexual activity and exposure to needles and blood, the Haitian connection has always been somewhat mysterious and more difficult to explain.

Elimination of the Haitian listing from CDC's AIDS surveillance report, without official explanation, initially appeared equally difficult to understand, with few outside the agency aware of the change or what it meant.

The March 25 report on the 8,840 AIDS cases in this country indicated that Haitians comprised 3 percent of the cases, along with homosexual or bisexual men (74 percent), intravenous drug users (17 percent), hemophiliacs (1 percent), heterosexuals who had contacts with persons at risk of AIDS (1 percent), persons who received transfusions of blood products (1 percent) and none of the above.

But the Haitian listing was dropped without notice in the April 2 report. The Haitian cases were incorporated into the "none of the above" category, with an asterisk noting only that the category included "285 persons born in countries in which most AIDS cases have not been associated with known risk factors." Sources indicated that 284 of those cases involved Haitians and one an African immigrant.

CDC officials yesterday sought to minimize significance of the change, saying it represents an internal decision reflecting new understanding of the ways that AIDS is spread and new studies about the Haitian connection with the syndrome.

"The whole list was based on what one does," said Dr. Walter Dowdle, head of the CDC's Center for Infectious Diseases. "The one thing that stuck out was the Haitians, who were listed not because of what they did but what they were. That has always bothered us."

Acknowledging political pressure to change the listing, he said that did not play a role in the decision.

Dowdle and other CDC officials said recent Haitian immigrants are still thought to have a greater risk of incurring AIDS than does the general population. For now, they said, they have no plans to change recommendations that included Haitians among high-risk groups urged not to donate blood.

By taking Haitians off of the weekly report, "we acknowledged that we don't know the risk factors for the majority of them. Heterosexual transmission is a logical guess," said Dr. James Curran, head of the CDC's AIDS task force.

He and others said the action recognizes two other factors: that AIDS is occurring in central Africa and elsewhere among persons outside known high-risk groups and that American Haitians' exposure to the virus thought to cause the disease is lower than earlier expected.

Among studies scheduled to be reported in detail at a forthcoming international AIDS conference is one by New York's Downstate Medical Center in collaboration with the National Cancer Institute.

It found an "extremely low rate" of exposure to the AIDS antibody among healthy Haitians -- less than 5 percent, one of its authors said. In comparison, rates among homosexual men and intravenous drug abusers in the New York City region have been found to be in excess of 50 percent.

AIDS researchers said yesterday that another new study of AIDS cases among Haitians in the United States indicates that promiscuous heterosexual activity plays an important role, including contact with heterosexual prostitutes. So did an earlier study in Haiti, which found that bisexual activity and exposure to unclean needles play a possible role.

The findings suggest that being Haitian is not a risk factor, said Dr. Jean-Claude Compas, a Haitian-born physician affiliated with Downstate Medical Center and chairman of the Haitian Coalition on AIDS.