The 6-year-old AIDS epidemic came of age last week as a social and political issue.

One sign was the sheer numbers at the Third International Conference on AIDS at the Washington Hilton, the largest scientific meeting ever held on a single disease. The 7,342 scientists and health-care workers who attended more than doubled the count at the 1986 AIDS conference in Paris.

"When I think that in 1981, we had a hard time getting a conference of 50 or 60 people together on AIDS, the interest in this conference is very gratifying," said Dr. Frank Young, commissioner of the Food and Drug Administration.

Another sign was diversity. The Third International Conference on AIDS brought together scientists and lay people, virologists and counselors, epidemiologists and economists, immunologists and ethicists. There were as many sessions on human behavior as on cell biology, as much concern about how to reach drug abusers as about how to activate T-cells.

Still another sign was the way politics intruded on a meeting dedicated to research and rational, nonpartisan discussion of a modern-day plague.

The conference was barely under way when District police, wearing bright yellow rubber gloves, arrested 64 demonstrators outside the White House during a protest against the Reagan administration's call for more "routine" testing for AIDS. Attorney General Edwin Meese later told a meeting of police chiefs that police should wear rubber gloves when handling people at high risk for AIDS.

President Reagan himself, in his first speech on AIDS in the six years of the epidemic, had been booed at a dinner on the eve of the conference, as was Vice President Bush when he advocated increased AIDS testing in his keynote address.

By contrast, Dr. Edward Brandt, chancellor of the University of Maryland's Baltimore professional schools, received thunderous applause during his summary speech at the meeting's closing session when he declared, "We cannot let AIDS become a political toy."

Minutes later, Dr. Otis R. Bowen, secretary of Health and Human Services, was hissed and booed when he pledged the Reagan administration's intention "to remain in the forefront of the AIDS issue" and said AIDS had "the president's complete attention."

The conference itself generated little sensational scientific news. It was less a forum for scientific bombshells than a record of incremental steps of research progress. Collectively, the five days of speeches, papers and exhibits offered a relentless reminder of the dimensions of the global challenge of AIDS.

"We expect no breakthroughs to be reported here," Dr. George Galasso, conference chairman, said as the meeting opened, and he proved correct.

Two years ago, at the first international AIDS conference in Atlanta, recalled Dr. June Osborn, dean of the University of Michigan School of Public Health, the general atmosphere was one of "shock" at the fearsome new retrovirus. Last year at the Paris meeting the dominant sense was "gloom" about the steadily worsening scourge of AIDS.

This year, Osborn sensed "restrained but real optimism" on the part of scientists at the conference, a feeling that the AIDS epidemic "is not so awesome as to be beyond control."

The roughly 250 papers presented at the conference documented "sound and careful progress," though "nothing we have learned suggests that the vaccine problem will be easier than we thought it would," she said.

At least this year, there were "no rude or shocking surprises" reported at the conference, she said. With an epidemic as new and frightening as AIDS, that in itself is a kind of progress.

Though Dr. Robert Gallo, one of the first to identify the AIDS virus in 1984, reported a new AIDS-related virus identified in 10 Nigerians, he emphasized that it did not yet pose anywhere near the threat that the original AIDS virus does.

"This time at least we are ahead of the game," Osborn said. "This time we can be braced and ready."

Through universal and increasingly reliable testing of all blood donations in the United States, the risk of being infected with the AIDS virus from a blood transfusions has now been reduced far below the risk posed by medical illnesses that require blood transfusion.

What's more, the panic over AIDS has been blunted by careful scientific investigation showing that the virus can be transmitted only through sexual intercourse, the sharing of contaminated needles or other direct exposure to infected blood -- not through casual contact or by donating blood.

The lesson of the conference is that "good data make good ethics," Osborn said. "It is a wonderful and merciful fact of this epidemic, that public health and human rights are, as it turns out, best served by the same approaches."

The conference went beyond pure science and the traditional American search for a "technological fix" to address every aspect of the AIDS epidemic -- social, economic, educational and political.

In one sense, the societal challenges posed so starkly by the AIDS epidemic are not new. They have been raised, if less dramatically, by every other infectious disease.

"The only new thing about the AIDS virus is the virus itself," Osborn said.

"We're rediscovering what we were doing a generation ago with syphilis and other sexually transmitted diseases before they were even called sexually transmitted diseases," said FDA Commissioner Young. "People have forgotten the principles of controlling infectious disease -- all that lore and science."

Pride in the pace of scientific research on AIDS -- which is caused by a retrovirus that four years ago had not even been identified -- is tempered by the knowledge that changing risky human behavior is at least as difficult as devising a vaccine.

"I am struck by how little is know about human sexuality, drug abuse and other risk-taking behavior" that are crucial to the spread of AIDS, said Dr. Lars Olaf Kallings, chairman of next year's AIDS conference in Stockholm.

Even education -- society's most effective weapon against AIDS so far -- is fraught with complexity.

And particularly in urban areas, AIDS is inextricably tied up with other socioeconomic problems, including poverty, racism, unemployment, illiteracy, teenage pregnancy and poor access to health care, said the Rev. Carl Bean, of the Minority AIDS Council in Los Angeles.

Reaching the inner city poor and the minorities who are at disproportionate risk of AIDS requires different techniques than reaching middle class whites, he said.

"If you want to get to the drug addicts, use a recovering addict, not a Phd," Bean said. "If you want to get to the prostitutes, use someone from that community, not someone from UCLA."

Cross-cultural warnings about AIDS have to be carefully designed with the target audience in mind, agreed Gloria Rodriguez, of the New Jersey Department of Health, who said the fast-growing Hispanic population has been overlooked by most public health campaigns.

One-third of the Hispanic population in the United States is under 15 years old, she said. Forty percent of hispanic families are headed by women, and half of those are below the poverty line.

And in the Hispanic culture, Rodriguez warned, telling a woman to "be prepared with condoms" is another way of saying, "You're a loose woman."

No other health issue so entangles scientific and societal issues, said Dr. Samuel Broder, chief of clinical oncology at the National Cancer Institute. The only historical parallel he could think of, he said, is "maybe the development of the atomic bomb -- but we didn't know it at the time."

Testing for the AIDS virus is a volatile political issue raising difficult questions of cost, confidentiality and individual rights. Most public health experts support increased voluntary testing but worry that mandatory testing will drive underground the very groups it is aimed at -- those at high risk for AIDS, including gay men, intravenous drug users, prostitutes and others.

Testing has been mandatory for military recruits since 1985, and the Senate has unanimously passed a bill requiring testing of new immigrants to the United States. Beyond that, proposals to expand testing are highly controversial.

One problem with testing is that there is no effective treatment, let alone a cure, for those who test positive for the AIDS virus. At least one-third to one-half of them will come down with AIDS.

With no available cure or vaccine, public health officials must rely on the only weapon they have against AIDS -- education and behavior changes to curtail unprotected sexual activity and sharing of intravenous needles.

Simply knowing one's test result, several studies have suggested, is no guarantee that one will alter one's behavior to slow the spread of the virus. And the essential public health message stays the same, regardless of the test result.

"Let's say you test positive," said Dr. Reed V. Tuckson, the District's Commissioner of Public Health. "I tell you to stop screwing around, and if you do, use a condom.

"On the other hand, let's say you test negative. What do I tell you? Stop screwing around, and if you do, use a condom.

"What's the difference?"