An injection of two drugs normally used to treat HIV patients completely protected monkeys from becoming infected with the AIDS virus, researchers said yesterday. While it is too early to tell whether people can pop a pill and escape infection, the study provides the strongest evidence yet that it might be possible.

Dr. Walid Heneine of the Centers for Disease Control and Prevention studied rhesus monkeys that were injected with a version of Truvada and Emtriva. For 14 days, the monkeys were then exposed to a combined human-monkey AIDS virus.

The six monkeys that received the drug combination were all completely protected from infection. By comparison, nine monkeys that took part in a previous experiment all eventually became infected with the SHIV virus.

The researchers cautioned the drug dose was slightly different from that seen in people taking Truvada and said studies under way will answer the question of whether the findings will translate to humans.

The CDC noted that Truvada was highly effective in suppressing the AIDS virus in people already infected. It is not a cure but is among the drugs that can help keep HIV patients healthy.