The Department of Health and Human Services is expected to announce approval today of the first commercial test to help prevent spread of the AIDS virus through the nation's blood supply, government sources said yesterday.

They said Food and Drug Administration approval is expected to go first to Abbott Laboratories of North Chicago, one of five companies vying to market what may become one of the most financially lucrative laboratory tests in use.

Proponents say that the test for the presence of antibodies to AIDS (acquired immune deficiency syndrome) is a highly accurate, sensitive means of making an already safe blood supply even safer. But critics worry that the test may create turmoil for tens of thousands of Americans each year who either falsely test "positive" for the antibody or who have the antibody -- a sign of past exposure -- and must live with that uncertain prospect.

Blood transfusions and blood products used by hemophiliacs are linked with about 2 percent of the nation's AIDS cases. To date, more than 8,300 individuals have contracted the disease, and nearly half have died. But recent estimates suggest that as many as 400,000 Americans may have been exposed to the AIDS virus.

FDA and other experts stress that the new blood test is "not a test for AIDS." It measures only the presence of antibodies, but does not provide a means of predicting whether a person will become ill with AIDS in the future.

Recent evidence from the Centers for Disease Control and other researchers suggests that infected persons may carry the virus indefinitely. Rough estimates suggest that 20 percent to 30 percent may later become ill with symptoms of lymph node involvement, fatigue and weight loss, and 10 percent may come down with the actual disease, which attacks the immune system and makes its victims vulnerable to life-threatening infections and cancer. There is as yet no reliable treatment or cure.

A growing number of critics, from state and local health officials to homosexual-rights groups, have expressed concern about the test's accuracy, its interpretation for those who test positive, and its possible uses for purposes other than screening blood donations.

There also has been concern that individuals in high-risk groups, such as sexually active homosexuals, might donate blood to find out whether they have been exposed to the AIDS virus, but the government has pledged to work with local officials to provide alternative testing for that purpose.

A two-week delay in expected government approval has allayed many of the fears, as officials from the FDA and CDC met publicly and privately with affected groups to work out plans for implementing the test and educating the public about its value and limitations.

FDA commissioner Frank Young met recently with representatives of homosexual-rights groups, who said yesterday that they received assurances that the labeling of the test would emphasize that it was primarily for blood screening and not for diagnostic purposes.

Nancy Langer of the Lambda Legal Defense and Education Fund, a New York homosexual-rights organzation, said yesterday that her group, which filed a petition Thursday to the FDA to postpone licensing, was pleased with the meeting but is "still considering whether to file a lawsuit" because of concern about the accuracy of the test.

At a day-long meeting on Feb. 22, Abbott officials presented data showing that their test was99.8 percent effective in ruling out the presence of AIDS antibodies. It is not certain what proportion of the remaining 0.2 percent may be "false positive" laboratory readings. Although the positive test rate is small, the numbers of individuals involved could be high: tens of thousands annually because of the number of blood tests involved.

There also has been concern about how many cases of AIDS virus infection might slip through the screening process. Abbott said that its test was 95 percent effective in picking up readings from individuals who actually have AIDS.

Dr. Gerald Sandler of the American Red Cross said yesterday that if approval is given Saturday, the blood-collecting agency will begin immediate negotiations to buy the test and perhaps begin testing blood as soon as next week. His agency, which collects about half of the nation's blood donations, and other blood banks plan to phase in use of the test over the next several weeks. Blood that is "positive" for AIDS antibodies will discarded as soon the testing starts, but notification of donors of "positive blood" will not begin until after this first phase is completed.

In addition to an estimated million tests a month at blood banks, the test also will be used to screen blood plasma collection, which totals about 10 million units each year, and will be available in "alternative test sites" ranging from clinics to physicians' offices for individuals who may wish to have the test.