Unless improvements are made, more than half of all young black men who are gay or bisexual will be infected with HIV within the next decade, according to findings presented Monday at the 19th International AIDS Conference.

The 2009-10 study of 1,553 American black men who have sex with men found that among those who are age 30 or younger, the infection rate was nearly 6 percent a year.

The overall rate of new HIV infection among all black gay and bisexual men in the study was 2.8 percent a year — nearly 50 percent higher than among white gay and bisexual men. The study was conducted in six cities, including Washington.

If those infection rates are projected over a decade, one-third of all gay and bisexual black men will have HIV infections, as will more than 50 percent of young men in that group, said Kenneth H. Mayer, one of the lead researchers. Mayer is an AIDS specialist and medical research director of the Fenway Institute in Boston.

“These study results show that in proportion to their numbers, black men who have sex with men are bearing the brunt of the HIV epidemic here in the United States, even in comparison to other groups of gay and bisexual men,” Mayer said in a statement.“We found that the men had many unmet medical and social service needs.”

Most of the men in the study who were newly diagnosed with HIV were unemployed, and nearly all had annual household incomes under $50,000.

“This is a clarion call to public health officials,” Mayer said.

The focus on disparities in infection rates is one of the major themes of the conference, which opened Sunday and runs through Friday.

In Monday’s opening plenary session, Phil Wilson, president and chief executive of the Black AIDS Institute, said that “black men are engulfed in a raging epidemic.” The odds that a gay black man will get infected are even worse. By the time a gay black man is 40 years old, “there is a 60 percent chance he will be HIV-positive,” said Wilson, who called himself a “three-fer:” gay, black and HIV-positive.

In the United States, new HIV infections among the general population have remained stable at about 50,000 a year, according to the Centers for Disease Control and Prevention. But because people are living longer with HIV, the epidemic in the United States is growing, and a person’s chance of meeting a sexual partner with HIV is also greater, especially in demographic subgroups where HIV prevalence is high, such as among black gay and bisexual men, said Jonathan Mermin, director of HIV/AIDS prevention at the CDC.

“That makes the prevention job harder every year,” he said.

More research is focusing on black men who have sex with men, especially the young. Black men who have sex with men make up less than 1 percent of the U.S. population but constitute more than 25 percent of new HIV infections, researchers said.

The study in 2009 and 2010 by the HIV Prevention Trials Network looked at black gay and bisexual men in Atlanta, Boston, New York, Los Angeles, San Francisco and Washington.

In Washington, 2.7 percent of the population is living with HIV, a prevalence rate that is among the highest of any large city in the country. Among blacks, who make up just under half the population, the leading cause of HIV transmission is heterosexual sex.

But Washington is a destination city for gay black men, and health officials said the new findings will help them better target testing and treatment toward those networks.

The most recent D.C. data show there were 76 newly diagnosed HIV cases in 2010 among white men who have sex with men, but more than twice that many —186 — newly diagnosed cases of HIV among black men who have sex with men.