WASHINGTON -- Development of a vaccine to prevent AIDS is finally gaining momentum, advocates say, but an effective vaccine -- the best hope for fighting the deadly disease -- is still years away.

"Enormous progress has been made," said Seth Berkley, president and chief executive officer of the International AIDS Vaccine Initiative, a New York nonprofit group. "There are many players involved, and there's a new sense of collaboration. People are working in 22 different countries."

Still, "the involvement is like a drop in the bucket" compared with the magnitude of the AIDS epidemic, which already has claimed 20 million lives, Berkley said earlier this month during an AIDS panel discussion sponsored by his group. And despite progress on vaccine development, he added, "there hasn't been enough attention focused on a vaccine."

AIDS vaccines account for less than 1 percent of global spending on pharmaceutical research and development, according to the initiative. Attempts to develop AIDS vaccines gained steam only in the late 1990s.

Vaccine development has been particularly tricky due in large part to the nature of HIV, which infects and kills the immune cells that fight diseases -- the same cells a vaccine must mobilize to prevent HIV infection.

Complicating matters, the virus is a moving target for vaccine developers, constantly changing its surface makeup.

Several proposed vaccines already have failed initial tests and several more are in various stages of development and testing. Pharmaceutical giants like Merck, GlaxoSmithKline and Aventis Pasteur have recently announced sizable vaccine programs and new support for research is coming from a combination of foundations, governments and multilateral agencies.

Today, nine initiative-sponsored human trials of a preventive AIDS vaccine are under way around the world. Small-scale trials are taking place in the United Kingdom, Kenya and Uganda. Separate trials are under way in Thailand, and new trials are set to begin soon in India and China.

Pilot programs in Kenya and Uganda have earned support from local communities, said Chrispin Kambili, regional medical director of the initiative's East Africa office in Nairobi, Kenya.

"Things are going well; this is doable," Kambili said. "We are currently building infrastructures [necessary for vaccine trials] in different sites. We are mobilizing communities and developing a sense of ownership and respect among participants."

In February, results were announced for the first-ever phase III AIDS vaccine trial -- the type that might lead to a decision to market a vaccine and begin production -- that involved 5,400 volunteers from the Americas and the Netherlands. That vaccine, known as Aidsvax and developed by a California biotech firm called VaxGen, failed to trigger the desired immune system response, however.

"It did not show efficacy, but the trial itself was a success. It really proved that a vaccine trial could be done [among larger groups]," Berkley said.

Even if a vaccine is proven effective, some fear that resources for mass production may not be readily available.

Manufacturing capability is limited even for current vaccines, said Andreas Neubert, manager of Vaccine Production at IDT, a German biotechnology firm. New facilities and technologies would be needed to produce millions of doses of AIDS vaccine.

Developing the vaccine itself could easily take a decade, Neubert said, and that normally would provide plenty of time for building such a plant. But the need for the vaccine is so great that work on this infrastructure must get under way soon. He estimated it will take $300 million to $350 million to develop a large-scale plant.

The United States took the lead when President Bush asked Congress to provide $15 billion over the next five years for programs that would provide anti-retroviral drugs to AIDS patients, work to prevent new infections and ensure care to children orphaned by the disease.

The International AIDS Vaccine Initiative spends roughly $30 million annually on research to develop an AIDS vaccine. In all, the world spends between $540 million and $570 million annually, a five-fold increase from five years ago, according to the group.