When the 17-member committee makes its recommendation Wednesday - advice the FDA does not have to follow but typically does - the ban could be lifted or relaxed, or not changed at all.

An advisory committee to the Department of Health and Human Services recently recommended replacing the ban with a 12-month deferral period for men who have had sex with men in that time.

In that case, sexually active gay men would still be prohibited from donating blood, but those who have not engaged in sex with other men in the past year would be allowed to donate.

Jason Cianciotta, director of public policy at Gay Men's Health Crisis, said such steps would not eliminate the stigma or discrimination associated with the ban on gays.

"While the proposed change from a lifetime ban to a 12-month deferral is a step forward, it does not go far enough," he said during the public comment portion of the FDA advisory meeting near the US capital on Tuesday.

"Any deferral based on a sexual orientation label - MSM (men who have sex with men), gay or bisexual - still perpetuates the harmful and unscientific notion that HIV is transmitted because of who you are rather than what you do." He also described a policy requiring 12 months of abstinence as a "de facto lifetime ban" for most gay and bisexual men.

"We advocate for a system that screens all donors, gay or straight, for high-risk practices that could lead to HIV infection," he said.

However, critics called on the panel to reject any move that could increase the risk of HIV in the blood supply.

"I urge you to oppose any change," said Peter Sprigg, senior fellow for policy studies at the Family Research Council, a conservative group.

"Unless it can be scientifically proven that a revised policy would result in no increase in risk to the blood supply. Even a small increase in risk is unacceptable," he told the committee.

"Let us not forget the dramatic magnitude of the increased HIV risk in this population."

Glenn Cohen, a law professor at Harvard University, argued in a recent editorial in the Journal of the American Medical Association that the United States was lagging behind other developed nations like Japan, Britain and Australia, which allow for gay blood donations after a 12-month period of sexual abstinence.

South Africa requires a similar period of abstinence for potential blood donors, regardless of their sexual orientation.

Even though there is a short window of time right after HIV infection when tests may not come back positive, scientists tend to agree that a period of one year is largely sufficient to assure that a person was not infected following potential exposure.

A 2010 study by the University of California, Los Angeles estimated that a complete end to the ban on gay blood donations in the United States would raise the total amount of blood collected just two to four percent.