STOCKHOLM, Sweden (AP) _ Tacked on row upon row of bulletin boards that zigzag across the floor of three echoing conference halls are 3,200 battle reports from the medical war on AIDS.

Each is a separate scientific study - a ''poster,'' in the jargon of scientific meetings - that offers some new insight, however slight, into the life of the AIDS virus and the people it kills.

Researchers stand in front of graphs and diagrams and large-type summaries of their work, ready to offer the browsing crowds of researchers more details about their discoveries: how the virus's genes work, why the body's natural defenses fail, how the germ spreads across continents and what miseries are inflicted upon the bodies of people who harbor it.

The crowd is microbiologists, sociologists, epidemiologists, virologists, medical ethicists and more, all joined by a common concern that has brought together 7,000 people from 138 countries for the Fourth International Conference on AIDS.

''There is good news on one side and bad on the other,'' said Dr. Stephen Rossner of Stockholm's Karolinska Hospital as he glanced through the posters.

''The number of victims is increasing, but it is also clear that there are many new approaches and potential ways to attack the virus,'' he said. ''The mood is one of reality. Nobody expected any breakthroughs to come out, but so many people are struggling, and that is good.''

Despite the daunting volume of new information at the meeting, none of it suggests that a cure or effective vaccine will be ready soon.

''When you work with people infected with AIDS, it's disappointing that the research is not progressing more rapidly,'' said Ann Fosberg, a research associate at the New England Area Comprehensive Hemophilia Center in Worcester, Mass.

''They are asking us for cures and vaccines,'' she said. ''It's difficult to tell them that we are learning, but very slowly.''

The time of rapid advances is over in the brief history of AIDS. The easy discoveries, it seems, have already been made.

''Nobody comes to these meetings expecting to be regaled by a series of major breakthroughs, and that's certainly true this time,'' said Dr. Franklyn Judson of the University of Colorado. ''The breakthroughs are behind us. Things are getting deeper and more complex. Our understanding is coming in smaller and smaller steps.''

Even though most of the news at the meeting is bad, the collective personality of the gathering is not as depressed as the grim data might warrant.

In fact, says Judson, ''the mood is still optimistic, because that's the outlook of people who are involved in this field. You have to be an optimist to stay in it.''

Besides the posters, scientists at the meeting tell of their findings in 383 oral presentations. Usually nine sessions, all of them in English, take place at the same time on subjects ranging from experimental vaccines and drugs to sex education and the impact of AIDS testing.

The urge to look at the bright side often comes through in these talks. For instance, when Dr. William Haseltine of Dana-Farber Cancer Institute in Boston told of the discovery of a ninth AIDS viral gene - something that makes a dauntingly complex subject even harder to understand - he stressed that all these genes provide potential targets for new drugs.

Even though much of the science concerns AIDS on the microscopic level, there are also reminders of the ultimate subject of all this discussion - the victims.

As people enter the conference center, the first thing they see is four large multi-colored pieces of cloth. Four more hang in the main conference hall. Each contains the name of eight people who have died of AIDS.

They are part of the Names Project quilt. The rest of it, nearly 4,000 names in all, is on a tour of U.S. cities.

Although the tone of the meeting is almost unremittingly serious, there are occasional light moments.

One morning, for instance, Bleach Man strolled down a hallway. He wore a costume something like Superman's, but had a bleach bottle for a head.

With him, Dominic Capello of the San Francisco AIDS Foundation explained that back home, Bleach Man walks through city neighborhoods, telling drug addicts how to sterilize their needles with bleach to prevent spreading the virus.

Nearby, scientists wandered through the commercial exhibits, looking at brochures handed out by various public health organizations, advocacy groups, journal publishers and manufactures of AIDS testing kits and drugs.

At one of the booths, a crowd gathered every few minutes to watch a British condom producer pump one of its products full of air. The idea was to prove that they don't leak.

The scientists stared in fascination as the condom grew to the size of a watermelon, then popped with a sharp bang.