Though Cuba has experienced severe economic difficulties, President Fidel Castro has long invested heavily in Cuba's scientific establishment, hoping to use inventive discoveries as proof of the fruits of socialism.

After a third dose of one new vaccine, say Cuban officials, it appears that it shows no ill effects on its hosts. An August conference in Havana found researchers Carlos Duarte and Felipe Rolo promising to continue experimenting with their findings for at least four more years. The Cuban researchers began their work in 1991 and say that their testing still remains in its early stages.

The study utilized 24 HIV-negative male volunteers who took the vaccine, which is based on a recombinant protein produced by a lab-generated gene forged from genes which link with different strains of HIV.

The recombinant protein includes the most significant characteristics of between nine and eleven strains of the HIV virus. This fact gives the new vaccine promise, the scientists believe.

Genetics play, it appears, a significant role in vaccine-making. A second "anti-AIDS gene" has been discovered by scientists at the National Cancer Institute whose work appeared in the journal Science. The results of tests on 3,000 subjects have confirmed the existence of a second mutation that reportedly inhibits disease progression.

This finding, say scientists, means that there are, likely, more such genes that help protect against the virus.

Vaccine tests in Denver, Colorado have also been launched, in a program using 30 high-risk volunteers, all HIV-negative gay and bisexual men.

Denver is just one of fourteen locales where a larger study called Project WIN, is currently testing a total of 420 volunteers with two "first generation" vaccines made by pharmaceutical companies. The volunteers are, uniformly, persons who are not yet infected with HIV, but who continue to exhibit risk factors that could lead to infection.

One of these vaccines, tested on 350 men shows, say scientists, no serious side effects. The second vaccine, also tested on subjects without ill effects, has drawn 600 volunteer subjects.

The emergence of vaccine studies marks the first time in three years that health officials have given attention to preventive measures. Previously, because of the complexity of the AIDS virus, the making of vaccines was not thought practical.

Many AIDS activists believe that the focus placed on vaccines by the Clinton Administration is wrong-headed, and that scientific investigators would be best advised to seek instead for a cure.

Dr. Frank Judson, director of the Denver Public Health project, says that it will be years "before we develop a vaccine that will be able to not only stimulate both cellular and antibody immunity but also will be safe."

Judson is satisfied that vaccine research is significant, however. "This means that clinical research on HIV vaccines is getting back on track after three years during which very little has happened," he said.