San Francisco ? The failure of an experimental AIDS vaccine in its first major test has shattered hopes of developing a shield against infection in the near future and demonstrated just how far scientists are from bringing the disease under control.

Still, the results made public Monday contained an intriguing finding: The vaccine appeared to work well in the small number of blacks who participated. Scientists said more study is needed to draw any conclusions.

The drug’s developer, Vaxgen Inc., said that overall there was no meaningful difference in protection between the 3,330 volunteers who received the genetically engineered vaccine and the 1,679 volunteers who received a placebo. All participants were at high risk of contracting the disease through sex.

Officials had been willing to give the drug approval even if it worked in just one in three people.

“The AIDS virus is really wily and mutates easily,” said Dr. Tom Coates, director of the AIDS Research Institute at the University of California at San Francisco.

Dozens of companies, universities and researchers are racing to develop their own vaccines. Among them: Merck & Co., GlaxoSmithKline and Aventis Pasteur. But none of those projects is considered as advanced as Vaxgen’s.

Vaxgen, based in Brisbane, Calif., has spent $200 million developing its AIDSVAX vaccine and said it remains hopeful the vaccine will someday help slow the spread of AIDS. Results from another big human experiment in Thailand are expected to be released later this year. The Thailand experiment involved IV drug abusers.

Vaxgen executives said they were encouraged by the results among the 314 blacks who participated in the study.

The experiment showed that there were 78 percent fewer infections among black volunteers who took the vaccine than those who received a placebo. Four of the 203 blacks who received the vaccine became infected, while nine of the 111 who received the placebo were infected. There were similar results among the small number of Asians involved in the study.