Finding 81 suitable volunteers for the nation’s first test of an experimental AIDS vaccine is taking longer than expected, but it should be done within the next three months, a federal health official said. Officials had earlier hoped to have all the volunteers injected by January, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. So far, 26 have been injected with the experimental vaccine in a test overseen by the institute, said Fauci. The study calls for 63 men to get the vaccine, and another 18 men to be injected with a substance that is not directed against the AIDS virus. Researchers are testing the vaccine only for side effects and for reaction of the immune system.