Many people with HIV infection do not tell their sex partners that they carry the virus that causes AIDS, potentially spreading the infection to unsuspecting mates, according to a Brown University study published today in the medical journal Archives of Internal Medicine.

Researchers interviewed 203 men and women who came to HIV clinics at Rhode Island Hospital and Boston City Hospital, both urban hospitals drawing patients from the inner city. Almost two-thirds said they were sexually active, and 40 percent of those who were having sex said they did not reveal their infection to their partners.

Dr. Michael Stein, the study's lead author, said his work "stands in sharp counterpoint" to reports last week that AIDS deaths are declining as new medications improve survival. "That's the good news," Stein said. "In my study, we learn the not-so-good news: that the risk of infections continues."