When a blood drive came to his office at the Library of Congress, Charles McMoore considered it his civic duty to make a donation.

He never got the chance. As soon as a blood collection worker looked at his questionnaire, he said, she curtly declared that he was unsuitable and told him to leave.

McMoore had answered yes to Question No. 14: Are you a male who has had sex, even once, with another male since 1977?

It didn't matter that he is HIV-negative and "healthy as a horse," said McMoore, 32, of the District.

Furious over the snub, McMoore filed a discrimination complaint with the D.C. Human Rights Commission--and promptly found himself drawn into an emotional debate over whether millions of gay men should become eligible to donate blood for the first time since the AIDS epidemic erupted in the early 1980s.

Since 1985, U.S. blood banks have been asking men whether they have had sex with other men to screen out risky donors and protect the blood supply. The spread of HIV--the virus that causes AIDS--among gay men has slowed, and today the rate of infection is increasing more rapidly among other groups.

But research indicates that gay men remain at high risk of spreading HIV. An estimated 8 percent of gay men nationwide are infected, federal officials say.

Critics say the wording of the questionnaire stigmatizes homosexuals, invites donors to lie and sends the wrong public health message to people in groups increasingly at risk of infection. The question asks about behavior stretching back 22 years, but government officials say they have yet to see HIV remain undetectable in the blood for more than one year.

"This question is one of these vestiges from the early years of the epidemic, when public policy was driven by ignorance," said Wayne Turner, of the D.C. chapter of ACTUP, an AIDS activist group. "Gay men are having sex, but they're having safe sex."

The Committee of 10,000, which represents hemophiliacs infected with HIV through tainted blood transfusions from 1978 to 1985, echoes that view.

"We agree with the gay community that it's discriminatory and unnecessary," said Corey Dubin, the committee's president and a member of a Food and Drug Administration blood advisory committee studying the issue.

"The issue isn't whether you're gay, but whether you are involved in risk behaviors associated with the transmission of the virus," said Dubin. "Obviously, the blood banks are petrified of asking donors if they have been having anal sex."

With blood donations nationwide projected to fall short of demand next year, officials are approaching the question gingerly, weighing new science against old fears.

Eric Goosby, a physician and director of HIV-AIDS policy for the U.S. Department of Health and Human Services, said he doesn't know when change might come.

"It is both a scientific and a political-social issue," he said, and any new policy would have to clear several federal committees and Surgeon General David Satcher before HHS Secretary Donna E. Shalala makes a final decision.

"To maintain a safe blood supply, you need to reject some donors who are perfectly healthy," said F. Blaine Hollinger, chairman of the FDA's blood products advisory committee. "There are some political issues, but what else is new? No one wants to be wrong."

The questionnaire asks about other behaviors that would disqualify a donor, but most of those questions go back only 12 months. Donors are asked, for instance, whether they have used drugs, contracted a venereal disease or had sex with a prostitute.

No mention is made of specific types of sex acts, whether condoms were used or whether the donor had multiple partners.

Among the 50 questions, the only ones that cover behavior going back 22 years are No. 14 and those that ask whether a donor has been a prostitute, an injection drug user, a resident of any of eight African nations or a recipient of blood products in those countries.

The U.S. blood supply today is safer than ever, and continual improvements in lab screening and conservative donor policies have reduced the risk of tainted blood transfusions. The situation is a far cry from the 1980s, when thousands of hemophiliacs and others who received transfusions died after being infected with HIV-tainted blood.

Today, the government estimates that 1 in every 600,000 to 1 million units of donated blood is HIV-infected and escapes detection to become part of the blood supply. That's fewer than 20 cases a year.

Blood banks have the technology to spot HIV in blood three weeks after a donor is infected. But the government is concerned that sexually active gay men might donate during that period when the virus is undetectable.

A sensitive new screening process, nucleic acid testing, may be able to close the window entirely when it is approved. But even with that capability, no technology can overcome human handling errors, so officials want to continue asking about donors' travels, sexual experiences, medical history and drug use.

"We just want to make sure there is no threat of risky units slipping through even the very elaborate safety net we have set up," said Richard J. Davey, chief medical officer for the American Red Cross, the nation's largest blood collection agency. Asked whether technology would take care of the problem, he said, "I don't see us being at that place for the foreseeable future."

Davey said he would be comfortable with a five-year exclusion for men who have sex with men. Celso Bianco, president of American's Blood Centers, a consortium of independent blood banks, believes a one-year exclusion is enough.

Yet everyone wants to keep asking questions--even though studies show about 2 percent of blood donors give false answers.

The debate is complicated by questions from FDA officials about whether the added number of donations is worth the extra risk. If the exclusion period were changed to five years, the FDA estimates, it would add 58,000 blood donations to about 11 million collected in a year--but it would also increase from 1,000 to 2,200 the number of tainted units that would have to be caught by lab screening.

If the period were changed to one year, it would yield about 112,000 more donations--but increase the number of tainted units to 3,000.

"You would take this double or triple risk, and the benefit you would get from it would be a less than 1 percent increase in the blood supply," Andrew Dayton, an FDA transfusion disease expert, told a blood panel in 1997. "I will just let that number stand for your consideration."

In 1997, Hollinger's committee decided the policy should be changed--but not just yet. They asked for more scientific data, but nothing has happened.

Activists aren't waiting. At Purchase College of the State University of New York, in Westchester County, an AIDS task force headed by a top campus administrator continues to block campus blood drives because it considers Question No. 14 discriminatory and misleading. The phrasing is misleading because it suggests that only gay men are at risk of being infected with HIV, said Ronald Herron, vice president for student affairs.

Gay students at the University of California at Santa Barbara have been protesting campus blood drives for the past year as a violation of the university system's anti-discrimination policy. They hope to bring lawsuits to bar blood drives on nine university system campuses until the questionnaire is changed.

In Canada, Quebec City gay rights activist Joel Pinon lied in May about his sexual activities and donated blood, and then announced the stunt weeks later. Officials tracked the recipients of blood products derived from Pinon's donation, found them to be uncontaminated, then destroyed what remained of the donation. The government threatened to prosecute him but has filed no charges.

Gay rights and civil liberties groups have not mounted legal challenges because they want to defer to the scientists. McMoore, the Library of Congress technician, settled his case with the American Red Cross after the group showed the D.C. Human Rights Commission that the policy comes from the federal government.

No group is as conflicted over the policy as the gay medical community. The 2,000 members of the Gay and Lesbian Medical Association are not sure what the new policy should be, said the group's former president, Michael Horberg.

"As a practicing HIV physician and primary care internist, I am quite torn," Horberg said. "As a gay man who is HIV-negative, I would definitely love to be able to perform my civic duty and donate. But I do understand the passions people have in this case and their desire to make sure the blood supply stays extra secure."

CAPTION: Charles McMoore is HIV-negative but has been rejected as a blood donor because he is gay. He says rules on blood donations are discriminatory.