WASHINGTON — Nearly 6 percent of black gay and bisexual men under age 30 are newly infected with HIV ­every year in the United States, three times the rate among white men of the same sexuality in the United States, accord­ing to the largest study ever to look at infection rates in this population.

The study, conducted in Boston and five other cities, was presented Monday at the 2012 International AIDS Conference. Overall, the infection rate among black gay and bisexual men over 18 was 1½ times the rate for their white counterparts, and the researchers said a lack of HIV testing in this population may be one reason.