ATLANTA – Most gay and bisexual men infected with HIV in the United States are taking steps to reduce the chances of passing on the deadly virus to their sex partners, according to a federal study released on Thursday.

A survey of 1,923 men who have sex with men found that 31 percent had abstained from sex with men in the previous year, the Centers for Disease Control and Prevention said in an article in its weekly morbidity and mortality report.

Among those who did have sex, 43 percent reported having only one partner, the CDC said. Men infected with HIV, the virus that causes AIDS, were also 3.5 times more likely to use a condom when having sex with an uninfected partner.

Gay and bisexual men account for a majority of the estimated 950,000 people infected with HIV in the United States. About 16,000 Americans die from AIDS each year, and another 40,000 contract HIV.

“These findings underscore the need to help HIV-positive individuals maintain safer behaviors over the long run,” said the CDC, which has made diagnosing and treating HIV-infected people the cornerstone of its AIDS prevention strategy.

But CDC researchers also noted that some gay and bisexual men were still engaging in high-risk sex.

Some 14 percent of those surveyed did not use a condom the last time they had insertive anal intercourse with an uninfected partner, while 25 percent did not use one the last time they had sex with somebody whose HIV status was unknown.

HIV-positive men are more likely to transmit the virus through anal sex when they are the active partner engaging in penetration rather than the passive partner receiving penetration.

Unprotected anal sex is considered to be one of the main routes of HIV transmission.

The CDC study was conducted between May 2000 and December 2002 in 16 states. Only gay and bisexual men who had been diagnosed with HIV for longer than 12 months were included in the survey.