A study challenges the popular belief that spermicides protect against AIDS and other sexually transmitted diseases.

The research, conducted on prostitutes in Cameroon, found no sign that combining the common spermicide nonoxynol 9 with condoms worked any better than condoms alone.The findings were first reported in Washington last year. They are now being published in Thursday's issue of the New England Journal of Medicine.

The study was conducted on 1,292 HIV-negative prostitutes and directed by Dr. Ronald E. Roddy of Family Health International of Durham, N.C.

The women were given condoms and were randomly assigned to get either a spermicide film or an inactive placebo film. They were told to insert the film into their vaginas before intercourse and to require their sex partners to use the condoms.

The study was conducted between March 1994 and December 1996. Just under 7 percent of women in both groups became infected with the AIDS virus during the course of the study.