A federal investigation has found that three patients of a Florida dentist with AIDS were all infected with strains of the human immunodeficiency virus extremely similar to that of the dentist -- but unlike other strains found in the community -- indicating that they were infected in his office.

The case, expected to be reported next week by the federal Centers for Disease Control (CDC), is significant because it has ignited a national controversy over whether HIV-infected health-care professionals should be restricted from performing surgery and other invasive procedures.

The CDC is debating new guidelines to deal with the question of whether infected doctors pose a risk to their patients.

But the latest findings raise the possibility that contaminated equipment played a role in transmission. The findings are likely to initiate a new look at the infection-control procedures of all doctors, dentists and other health professionals who practice invasive procedures in non-hospital settings.

Molecular sequencing studies of the viral strains of all three patients showed the strains to be very close to that of the late David Acer, a Jensen Beach, Fla., dentist who has since died of AIDS, but different from those collected elsewhere in the community, sources said. Those two facts indicate that it is unlikely that the three patients were infected elsewhere, sources said.

What remains unclear, however, is exactly how transmission of the virus occurred.

When only one infected patient had been identified -- Kimberly Bergalis, 22, who has since developed AIDS -- health officials thought that Acer had injured himself while operating on her and that his blood had mixed with hers.

Since the discovery of two other infected patients, however, speculation has also focused on the possibility of contaminated equipment as a source of transmission. None of the three patients had independent risk factors for HIV infection, again pointing to the dentist's office as the place where transmission likely occurred, sources said.

"One of the patients was an older woman in a longterm marital relationship who had never had a blood transfusion and whose husband tested negative," one source said.

Harold Jaffe, the CDC epidemiologist in charge of the investigation, refused to comment. But in an interview last November, Jaffe said that there had always been "questions about how the transmission actually occurred." He said then that the CDC was examining several possibilities, among them whether Acer had contaminated his equipment after working on his own teeth, or possibly after operating on one of his own sexual partners.