RESEARCHERS CAUTIOUSLY OPTIMISTIC ABOUT AIDS FINDINGS.

Byline: Lawrence K. Altman The New York Times

The 11th international AIDS meeting will open here today with leading researchers' hopes as high as the sun-drenched mountains surrounding this Canadian seaport.

Remarkable gains in using combinations of costly new and old drugs promise to slow the progression of AIDS, if not stop it in its tracks, and to allow many people infected with HIV, the virus that causes AIDS, to live longer and healthier lives, the researchers said in interviews.

Gains in prevention measures have helped avoid infection for many others in the United States, Thailand and some areas of Africa, offering hope that deterrents can work elsewhere. Health workers in Thailand calculate that by the year 2000 they will have prevented 2 million infections with HIV by controlling other sexually transmitted diseases that may increase susceptibility to AIDS infection and by educating people to practice safer sex. Their findings are among those to be presented to 15,000 participants from 125 countries at the conference.

New tests to measure the amount of HIV in the blood seem to be a better measure of survival than the widely used count of CD-4 immune cells. Other laboratory advances identifying co-factors that help HIV enter cells promise to help scientists unravel some mysteries about one of the wiliest viruses known.

By trumpeting the gains in glowing terms in advance of the meeting, a number of leaders in AIDS research and drug companies have transformed the pessimistic mood that has prevailed at the last several international meetings to one of exuberance. The mood change reflects testimonials from some AIDS patients who seem to have bounced back from their deathbeds, and statements from researchers testing a new class of anti-HIV drugs known as protease inhibitors in combination with AZT and other drugs in industry-sponsored trials. In recent months, the Food and Drug Administration has approved the marketing of three protease inhibitors: indinavir (Crixivan), ritonavir (Norvir) and saquinavir (Invirase).

One factor contributing to the optimism is a Canadian study showing the benefits of a combination of drugs (AZT, ddI and nevirapine) that did not include a protease inhibitor.

The effective combinations act on different enzymes at different sites in the virus to overcome the resistance that often develops to treatment with a single drug.

Preliminary findings of the first human trials reported in Washington in February showed that such combinations could suppress the amount of HIV in blood to levels that could not be detected by the latest laboratory techniques as long as 24 weeks after therapy begins.

The findings do not necessarily mean that the drugs can rid the body of HIV and cure AIDS, because the virus could still lurk somewhere in the body. Yet reports that virus suppression has been extended to nearly a year are expected to generate excitement. More important, experts said, consistent findings are coming from a number of investigators.

Nevertheless, not enough time has passed to determine how many infected people the combination therapies will benefit.

The line between excitement over genuine progress and false hope is thin. AIDS leaders who have worked in the field since the disease was first recognized in 1981 and who are usually cautious in their language are not playing down the gains. While trying to guard their optimism, they often have difficulty restraining their enthusiasm.

``We can't claim victory until the fat lady really sings,'' said Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md. ``She hasn't sung yet, but I think she is getting ready to sing.''

Fauci, like many other researchers and meeting officials, is wary of past experience in which initial hope about gains in AIDS research gave way to despair as early results later failed.

Dr. Martin Hirsch, a virologist at the Massachusetts General Hospital in Boston, said that as ``the nihilism has vanished and people have become enthusiastic,'' he and other leaders ``fear that we may be getting ahead of ourselves by delivering more hype than hope.''

Arguably the buildup to this meeting has been the biggest of any international AIDS conference. And AIDS experts caution that the wave of publicity could create false expectations.

Dr. Martin T. Schechter of Vancouver, a co-chairman of the meeting, said in an interview that the organizers wanted to overcome the ``doom and gloom'' atmosphere of the last several AIDS meetings when ``people would come with totally unrealistic expectations and go away bitterly disappointed when they failed to materialize.''

He said the risk was that people would fail to understand that ``the solutions were not going to happen tomorrow'' but that ``we were beginning to chip away at this thing.''

``AIDS is not the total despair it was five years ago,'' Schechter said. ``Our theme is tempered hope with a realistic sense of the challenges that lay ahead.''

CAPTION(S):

2 charts, map

Chart: (1) Children with HIV

(2) Estimated AIDS cas es

Map: Aids around the world

Associated Press