Despite overwhelming scientific evidence that a specific virus causes AIDS, a controversial researcher insisted yesterday before a panel here of the nation's foremost AIDS experts that the disease's cause remains unknown. The researcher, Peter Duesberg, is considered by many scientists as a gadfly who ignores facts in challenging the notion that the human immunodeficiency virus (HIV) causes AIDS. As he has done many times, he refused yesterday to acknowledge mounting evidence that associates HIV infection with AIDS.

Instead, Duesberg, a professor of molecular biology at the University of California at Berkeley and a pioneer in the field of cancer-causing genes, said AIDS is really caused by risky sexual behavior and drug use.

He gave no proof to bolster his claims. AIDS research has shown that HIV is passed through sexual contact, shared needles and from infected mother to fetus. Those activities, while capable of transmitting infection, do not by themselves cause AIDS.

"What kind of risk behavior does the infant born of an infected mother have?" asked Anthony S. Fauci, the coordinator of AIDS research for the National Institutes of Health. "And what about the 50-year-old woman who received a blood transfusion from an infected donor? The data overwhelmingly suggest that HIV is the cause of AIDS."

Duesberg, who is not an AIDS researcher, has made his assertions repeatedly in the last year and, for the most part, has been ignored by the scientific establishment. Although many AIDS researchers have refused to debate him, others said they decided it was time to confront his theories in public.

Yesterday's meeting, which was sponsored by the American Foundation for AIDS Research, was billed as a scientific forum on the cause of AIDS but was really an attempt to put Duesberg's theories to rest.

Several studies have shown that as many as 95 percent of those with AIDS were infected with HIV. Recent advances in laboratory technology should make it clear that the number is actually 100 percent, according to scientists speaking yesterday.

In addition, research has shown that, years before AIDS symptoms appear, the virus begins to ravage the body's immune system by invading and destroying cells most needed to fight off disease. After five years,, as many as 90 percent of those infected will have drastic irregularities in their blood system, even if they appear healthy, experts have shown.

"There is now enormous evidence that presence of the AIDS antibody is very bad news for the future health of any individual," said William Haseltine, chief of the laboratory of biochemical pharmacology at Boston's Dana Farber Cancer Center.

In one of the largest studies of the infection status of one city, researchers in San Francisco have found during the last three years that, among 578 people not infected with HIV, nobody has developed symptoms of AIDS. Of 435 who were infected, 55 have developed AIDS.

Duesberg said he bases his thesis that HIV does not cause AIDS on a belief that the virus fails to infect a large percentage of susceptible cells, lies fallow for years and does not kill cells.

"I say if you have antibodies to HIV and you are not in a risk group you don't have anything to worry about," Duesberg said. He would not specify what he meant by "risk group."

While homosexual men and intravenous drug abusers account for the vast majority of those with AIDS, heterosexually acquired infection is the fastest growing category of the disease.

Researchers have said that there is no longer scientific question that HIV kills cells and that many other viruses, including those that cause herpes and measles, can lie dormant before becoming active.

"If people believed him, it would be incredible how many deaths he would cause," said Roger Detels, professor of public health at the University of California at Los Angeles.

"There is too much real work to be done to have to deal with his crazy opinions," Detels added.