The Justice Department has begun an antitrust investigation of the American Red Cross centered on its exclusive contract to sell a possible new blood-scrubbing technology, The Associated Press has learned.

Competitors fear that if the Red Cross controls the new technology for scrubbing the AIDS and certain other viruses out of plasma, some of the smaller banks that provide half the nation's blood could be forced out of business.The nation's blood supply already is very safe, experts stress, because of numerous tests for infection. But scientists have been hunting ways to make it even safer, avoiding even the occasional infection that now slips through.

The military considered this new scrubbed blood, called SD plasma, enough of an advantage that it put an alternative improved blood program on hold to await it. Thus, the Pentagon was upset when manufacturer Vitex suddenly informed officials of its deal to sell only to the Red Cross.

The Red Cross vigorously defended its new contract Saturday. A spokeswoman said the charity was confident it had violated no antitrust laws and would respond quickly to recent Justice Department subpoenas.

Justice officials would not comment.

The Red Cross will sell SD plasma to nonmember blood banks, charging them an as-yet-undetermined markup to recoup its investment, including a $3 million loan to Vitex, said Brian McDonough, chief operating officer of Red Cross blood services.

Some scientists aren't even sure the technology is worth all the fuss.

The Food and Drug Administration has not yet approved SD plasma, privately saying it is not such a lifesaving product that it should sweep the market. An FDA advisory committee advised the agency last month that an alternative method of better blood testing, also awaiting FDA approval, is equally effective.

Scrubbed plasma "adds a certain degree of safety that regular plasma doesn't have, but it also has some potential downsides to it," cautioned Dr. Harvey Klein, transfusion chief at the National Institutes of Health. "I'm concerned that it might be aggressively marketed" without acknowledging the drawbacks.

The New York Blood Center developed the new technology, solvents and detergents that dissolve the fatty coating of such viruses as HIV, hepatitis B and hepatitis C, then wash them out of the plasma.

For years, a version of the technology has been used in drugs made from plasma, such as immune globulin or hemophiliacs' clotting factor. In 1994, the New York Blood Center created Vitex to sell it for cleaning whole plasma - transfusions that some 400,000 Americans get yearly after trauma or surgery.

Its problems:

- Only large batches of plasma can be scrubbed. Doctors generally prefer to limit how often hundreds of blood donations are pooled together, because if one sick donor was included then dozens of patients who received plasma from the pooled product would have been exposed to infection.

- The SD system removes only viruses coated by fat. Others, such as hepatitis A, are not affected, and pooled SD plasma in Europe was linked to a hepatitis A outbreak.

If a new AIDS-like virus suddenly emerged that has a coating of fat, SD plasma would catch it and save lives. If a new virus emerged without a coating of fat, the pooled plasma could expose millions of people, Klein explained. "That's the worry," he said.

The FDA is considering an alternative: Individually packaging each donor's plasma and freezing it for 90 days. Then retest the donor. This virtually eliminates today's blood-testing drawback that an occasional donor is so newly infected that tests don't immediately spot infection, Klein said.