The possibility of contracting AIDS through a blood transfusion is a terrifying one, and for a time it was a real risk. But you -- as a potential donor or recipient -- are entitled to know that the risk is past.

A reliable test for AIDS is now available and, as of last month, literally every pint of blood leaving the Red Cross banks has been tested. The Red Cross supplies more than 90 percent of the blood given in transfusion in Washington and its surrounding region. The remainder comes chiefly from hospitals' banks, which follow similar standards.

In the past two years, nine people in this region, five of them children, were infected with AIDS through transfusions. One infant died. It was an ugly episode. Hospital patients, and particularly the youngest of them, are owed every possible precaution against infection. The point of the story is that, in response to these infections, scientists and blood-bank administrators have worked out new procedures that have returned the safety of the blood supply to the level that it had achieved before AIDS appeared.

The test itself is a triumph of medical technology. Incidentally, as you listen to the debates over federal funds for medical research and whether they should be frozen, you might want to note that this test was developed at the National Institutes of Health.

The test has generated a degree of controversy, not because it's ineffectual but, to the contrary, because it's extremely sensitive. It is designed to flag any remote possibility of the presence of AIDS, which means that it will err on the side of caution and occasionally produce a false positive reading. AIDS is transmitted most commonly through homosexual contact, and some homosexuals have protested that, at the current degree of sensitivity, the test will needlessly alarm those donors for whom it reports false positives. That's a pretty minor objection, and can be disregarded. If you doubt it, think for a moment of the 15-month-old child in Warrenton who died last year of AIDS passed through a transfusion.

Before March, the Red Cross and most other blood banks routinely checked all donations for two infections, hepatitis and syphilis. Now there's a third check. As for the stigma attached to AIDS, the infected donor has a right to privacy but not to a point that allows him to infect others. The blood banks have for years kept registers of prohibited donors -- those with histories of hepatitis or syphilis -- and no one's rights are violated by it. Blood is one of the very few substances in daily medical use that cannot be synthesized. Recipients have to be able to trust the blood that they are being given -- and to trust the donors. That consideration prevails above any other.