An experimental vaginal gel has shown some promise in preventing infection from the AIDS virus _ the first study to offer hope that a microbicide may soon join the medical arsenal in the international battle against HIV, AP quoted Scientists as announcing today The results were not conclusive in this preliminary study, but they were welcome news considering the failure of other similar products. The multi-country study suggests a gel made by Massachusetts-based Indevus Pharmaceuticals Inc. cut HIV infection to a slight degree, a researcher said today at a medical conference. «This is the first study that now shows we have a promising candidate,» said Salim Abdool Karim, the South African researcher who presented the results. About 3,100 women participated in the study, which was designed mainly to test whether it was safe. The women were divided into four groups. One-quarter of them used the Indevus gel, which is supposed to block the AIDS virus from attaching to certain white blood cells.