Back in this country, the Food and Drug Administration is about to implement new rules recommending that any man who has had sex with another man in the previous five years be barred from serving as an anonymous sperm donor. The FDA has rejected calls from gay rights groups to scrap the provision, insisting that gay men collectively pose a higher-than-average risk of carrying the AIDS virus. Critics say the FDA should use a screening process that focuses on high-risk sexual behavior by any would-be donor, regardless of sexual orientation.