Interviews with 500 gay men throughout the District found that more than 40 percent were unaware of their diagnosis before the study, even though most had seen a doctor in the past 12 months, and more than a third did not know the HIV status of their last sex partner.

The study also shattered some stereotypes: Younger men generally had safer sex behaviors; men older than 30 were tested less frequently, used condoms less often and had more sex partners.

"This is a wake-up call," said D.C. Council member David A. Catania (D-At Large), 42, who is gay. "It's time for my generation to assume greater responsibility for themselves and their partners. Just because we escaped the epidemic of the 1980s doesn't mean we are immune."

As a result of the study, city health officials recommended Thursday that men who have sex with men get tested twice a year for HIV.

The study acknowledges that it "may underrepresent some groups" and that more studies are needed to reach a wider population.

The findings come as city health officials and their community partners have aggressively increased testing and condom distribution to address concerns about an epidemic rate of infection in the District. Last year, the city tested 95,000 people and handed out 3.5 million condoms.

Even so, the report found that more than 40 percent of those interviewed said they did not use a condom with their last sex partner. Although men of color used condoms almost twice as frequently as white men, the study found more men of color were HIV positive than white men.

The District was one of 21 jurisdictions to participate in the survey, funded by the Centers for Disease Control and Prevention, to learn more about behaviors that put people at risk for the disease. Even though the numbers for the District, collected in 2008, are high, city officials said the rates in other jurisdictions recorded in 2005 were higher, including San Francisco (24 percent), New York (25 percent) and Baltimore (40 percent).

"We have a serious situation here, but we've also had some success," said administration Director Shannon L. Hader, who was joined by Mayor Adrian M. Fenty (D) at a news conference to announce the report.

Overall, more than 3 percent of D.C. adults and teenagers are living with HIV or AIDS, although new AIDS cases and AIDS-related deaths have declined in the past four years, according to a report released last week.

"We know we have a ton of work left to do," said Fenty, who would not say what level of funding he would provide for HIV/AIDS programs in the budget blueprint he plans to present to the D.C. Council next week.

Participants in the study released Thursday were recruited at gyms, bars, restaurants and clubs frequented by gay men and interviewed at those locations in all four quadrants of the city. The study included only men who had sex with men in the previous 12 months. Of those interviewed, more than half (52 percent) were men of color.

Nearly 60 percent of gay men in the city living with HIV/AIDS are black, according to a 2008 study issued by the HIV/AIDS administration. Fewer than 35 percent are white, an indication that the prevalence rate among gay men in the study might be higher and compare less favorably with other cities if more black men were included in the study.

Ron Simmons, director of US Helping Us, an HIV/AIDS assistance and awareness group for gay black men, said the study was flawed because it targeted gay men at venues that do not attract black men.

"The men in that study tended to be more educated and made more money. It was not really a representative sample," he said.

Staff writer Darryl Fears contributed to this report.