A new test to detect the AIDS virus in blood soon will be commercially available and should be used to screen all blood and blood products, the Department of Health and Human Services said yesterday.

The test would help prevent transmission of AIDS (acquired immune deficiency syndrome) through blood transfusions and use of blood products by hemophiliacs. This accounts for about 2 percent of AIDS cases.

HHS Secretary Margaret M. Heckler called new Public Health Service guidelines for administering the blood test "an important step forward in meeting our responsibility to the American people. We expect the test to be widely available in blood collection centers and in clinics and private physicians' offices around the country within a very short time."

Despite the new test, cases of the deadly disease are expected to increase rapidly, with an additional 40,000 anticipated in the United States in the next two years, warned Dr. Thomas C. Quinn of the National Institute of Allergy and Infectious Diseases in an editorial in this week's Journal of the American Medical Association.

"This illness now ranks as one of the most serious epidemics confronting man in modern time," Quinn said. He noted that, in addition to the human toll of AIDS, which kills 80 percent of its victims within two years of diagnosis, its "economic impact" will be "staggering," with health-care costs exceeding $50,000 for each patient.

He said that, while the new test will reduce blood-transmitted cases, the spread of AIDS through sexual activity -- the predominant mode of transmission, particularly in homosexual men -- will not be stopped until a vaccine or effective treatment becomes available.

As of last Monday, 7,788 AIDS cases were reported in this country, with 3,687 resulting in death. About 2 percent were blood-related -- 106 through transfusions and 56 among hemophiliacs who received blood products to treat their disease.

A commercial test to detect the antibody to the AIDS virus is expected to be approved by the Food and Drug Administration "within a few weeks," said Dr. Lowell Harmison, the health official coordinating the government's effort against AIDS.

The test is expected to indicate that an individual has been infected with the virus but not indicate whether the individual is likely to incur AIDS.

Anticipating this, the Public Health Service yesterday issued "provisional" guidelines for administering the test, saying "all blood or plasma should be tested" for evidence of the AIDS virus, known as HTLV-III, and discarded if the test proves positive.

While there has been general agreement about the need for an AIDS blood test, health-care experts have debated how the test should be applied, particularly how to inform blood donors about "positive" results. This is complicated because a small percentage of tests are expected to be falsely positive.

A report in this week's JAMA by National Cancer Institute researchers found that the test was "highly specific and sensitive" and warned that confirming tests may be needed to verify positive results from the initial test.

The new government guidelines outline procedures for retesting, informing donors of positive results, maintaining confidentiality and medical followup for individuals whose tests result in positive findings.

The guidelines say that positive tests should be repeated before a donor is notified and that, if the repeat or other tests are positive, "it is the responsibility of the collection facility to ensure that the donor is notified."

They stress that it is "important to emphasize to the donor that the positive result is a preliminary finding that may not represent true infection. To determine the significance of a positive test, the donor should be referred to a physician for evaluation. The information should be given to the donor in a manner to ensure confidentiality of the results and of the donor's identity."

But yesterday, health specialists who had reviewed the guidelines complained that they had been developed without enough discussion about the tests' risks and benefits.