NEW YORK – To the dismay of gay-rights activists, the Food and Drug Administration is about to implement new rules recommending that any man who has engaged in homosexual sex in the previous five years be barred from serving as an anonymous sperm donor. The FDA has rejected calls to scrap the provision, insisting that gay men collectively pose a higher-than-average risk of carrying the AIDS virus. Critics accuse the FDA of stigmatizing all gay men rather than adopting a screening process that focuses on high-risk sexual behavior by any would-be donor, gay or straight.

“Under these rules, a heterosexual man who had unprotected sex with HIV-positive prostitutes would be OK as a donor one year later, but a gay man in a monogamous, safe-sex relationship is not OK unless he’s been celibate for five years,” said Leland Traiman, director of a clinic in Alameda, Calif., that seeks gay sperm donors.

Traiman said adequate safety assurances can be provided by testing a sperm donor at the time of the initial donation, then freezing the sperm for a six-month quarantine and testing the donor again to be sure there is no new sign of HIV or other infectious diseases.

Although there is disagreement over whether the FDA guideline regarding gay men will have the force of law, most doctors and clinics are expected to observe it.

The practical effect of the provision – part of a broader set of cell and tissue donation regulations that take effect May 25 – is hard to gauge. It is likely to affect some lesbian couples who want a child and prefer to use a gay man’s sperm for artificial insemination.

But it is the provision’s symbolic aspect that particularly troubles gay-rights groups. Kevin Cathcart, executive director of Lambda Legal, has called it “policy based on bigotry.”

“The part I find most offensive – and a little frightening – is that it isn’t based on good science,” Cathcart said. “There’s a steadily increasing trend of heterosexual transmission of HIV, and yet the FDA still has this notion that you protect people by putting gay men out of the pool.”

In a letter to the FDA, Lambda Legal has suggested a screening procedure based on sexual behavior, not sexual orientation. Prospective donors – gay or straight – would be rejected if they had engaged in unprotected sex in the previous 12 months with an HIV-positive person, an illegal drug user, or “an individual of unknown HIV status outside of a monogamous relationship.”

But an FDA spokeswoman cited FDA documents suggesting that officials felt the broader exclusion was prudent even if it affected gay men who practice safe sex.

“The FDA is very much aware that strict exclusion policies eliminate some safe donors,” said one document.

Many doctors and fertility clinics already have been rejecting gay sperm donors, citing the pending FDA rules or existing regulations of the American Society for Reproductive Medicine.

“With an anonymous sperm donor, you can’t be too careful,” said a society spokeswoman, Eleanor Nicoll. “Our concern is for the health of the recipient, not to let more and more people be sperm donors.”

However, some sperm banks, notably in California, have welcomed gay donors. The director of one of them, Alice Ruby of the Oakland-based Sperm Bank of California, said her staff had developed procedures for identifying gay men with an acceptably low risk of HIV.

Gay men are a major donor source at Traiman’s Rainbow Flag sperm bank, and he said that practice would continue despite the new rules.

“We’re going to continue to follow judicious, careful testing procedures for our clients that even experts within the FDA say is safe,” said Traiman, referring to the six-month quarantine.

The FDA rules do not prohibit gay men from serving as “directed” sperm donors. If a woman wishing to become pregnant knows a gay man and asks that he provide sperm for artificial insemination, a clinic could provide that service even if the man had engaged in sex with other men within five years.

However, Traiman said some lesbian couples do not have a gay friend they know and trust well enough to be the biological father of their child, and would thus prefer an anonymous donor.

Dr. Deborah Cohan, an obstetrics and gynecology instructor at the University of California, San Francisco, said some lesbians prefer to receive sperm from a gay donor because they feel such a man would be more receptive to the concept of a family headed by a same-sex couple.

“This rule will make things legally more difficult for them,” she said. “I can’t think of a scientifically valid reason – it has to be an issue of discrimination.”