Researchers are learning a lot about the sneaky ways the AIDS virus attacks the body, but the path to a vaccine against the deadly disease is still unclear.

In a meeting Monday of researchers from the AIDS Vaccine Clinical Trials Network sponsored by the National Institutes of Health, experts reported progress in some elements of vaccine studies. However, most acknowledged there is still a long and uncertain period of experimentation before the promise of a vaccine can be fulfilled."So far, there are only little bits and pieces of information of a specific response" to candidate vaccines, said Dr. Daniel P. Hoth, director of AIDS research at the National Institute of Allergy and Infectious Diseases.

He said that although favorable responses have been seen in some experiments, the research is still in a very early phase and fundamental questions still need answers.

In discussions at the meeting, researchers said they still were uncertain if a vaccine should be based on the whole AIDS virus, or on pieces of it.

Using viral parts, which are types of proteins, is considered a safer and more practical approach. Proteins from the virus pose no threat of infecting patients with the disease but could still trigger an immunity within the body against that particular protein, and thus, against the virus.

Also, proteins could be made artificially, an important consideration in mass producing a vaccine.

The problem, researchers note, is determining which proteins to use in vaccines to trigger an immune response.

Additionally, Hoth noted, it is not clear yet which of the complex of immune responses possible in the body are essential to protect against AIDS.