The study comes as the Food and Drug Administration is revising rules for the claims that manufacturers can make on how well condoms prevent sexually transmitted diseases.

Packages now must state: "If used properly, latex condoms will help to reduce the risk of transmission of HIV infection (AIDS) and many other sexually transmitted diseases." But revisions were ordered by Congress in 2000 amid pressure from conservative groups demanding "medically accurate" claims as to condoms' effectiveness.

Safe-sex advocates warn that changing the wording would undermine public confidence in, and use of, condoms.

At the time, there was solid evidence only on how well condoms prevent pregnancy, HIV and, in men, gonorrhea. Recent research has produced strong evidence condoms protect well against gonorrhea, chlamydia and herpes in both men and women, said Dr. Ward Cates Jr., president of the Institute for Family Health at Family Health International. This study adds HPV to that list, he said.

"This will help clinicians to counsel their patients about the effectiveness of condoms to reduce another of the sexually transmitted infections - if condoms are used consistently and correctly," Cates said.

The researchers invited 24,000 female students ages 18 to 22 at the Seattle university to be in the study. Starting in 2001, they followed 82 from before their first vaginal intercourse, testing the women for HPV with swabs of the cervix and other genital areas every four months. The women kept online diaries detailing each act of intercourse, including condom use and whether there was any genital contact without a condom.

Winer said previous HPV studies either showed no protection from condoms or were inconclusive. This one included only virgins and collected more details, and the computer diaries helped women be more honest about condom use than those in studies where people are interviewed about their sexual behavior, she said.

"This is about as ideal a study as you can get," said Dr. Tom Fitch, a San Antonio pediatrician and board chairman at the Medical Institute for Sexual Health, which stresses abstinence and monogamy as the only sure ways to prevent sexually transmitted infections.

Nevertheless, Fitch noted that some consistent condom users still were infected with HPV. Fitch and Kloser also suggested that the results in the real world - say, among poor, inner-city women - might be different from those with college women.

Fitch said several studies have shown that at most, 50 percent of people reported using a condom every time they had sex.