A research team says it has identified a portion of the outer envelope of the AIDS virus that could eventually bring scientists closer to developing a vaccine against the dread disease.

To date, a major obstacle to vaccine development has been the existence of many different strains of the Acquired Immune Deficiency Syndrome virus.Scientists have found that a vaccine effective against one strain does not necessarily protect against others, enormously complicating the process of finding an effective preventative agent.

But a research team from the Walter Reed Army Institute of Research, the National Cancer Institute and the Repligen Corp of Cambridge, Mass., said it has identified a portion of the viral envelope that appears to be identical from strain to strain and thus offers a potential target for vaccine development.

"This is one more piece of the puzzle that we've put together. It's one of the many research findings that has to come out to develop a vaccine, if it's indeed possible to develop a vaccine," Repligen scientist Scott Putney said in a telephone interview.

Putney said the finding does not alter the generally held view that a vaccine against AIDS is unlikely to be available before well into the 1990s, if then.

"This doesn't alter the time frame for development of a vaccine," he said.

The researchers' findings were reported in the July 15 edition of Science magazine.

The research team looked at a portion of the viral envelope called RP-135. The envelope is a chain of proteins that acts as the virus's outer skin.