A federal judge threw out a $15 million suit yesterday that had been brought by the parents of a 3-year-old Herndon boy who died of AIDS contracted through blood transfusions he received shortly after his premature birth at Georgetown University Hospital in January 1983.

U.S. District Judge Thomas A. Flannery ruled in a 31-page opinion that Georgetown University and the American Red Cross were operating under standard medical practices when they provided the blood, and that there was no reasonable way they should have known that the child could contract AIDS through the transfusions.

"No reasonable jury could find that the possibility of contracting AIDS from a blood transfusion was a material risk at the time Matthew Kozup received his three transfusions," Flannery said.

"As of January 1983, only a single case of possible transfusion-related AIDS had been diagnosed, and that only weeks before Matthew received the contaminated blood," Flannery wrote.

Flannery noted that there was no available test for AIDS contamination until May 1985 and that it was not until 1984 that the "medical community reached a consensus as to the proposition that AIDS was transmissible by blood."

Stephen Kozup, Matthew's father, said last night he had not been notified of Flannery's decision and that he had no comment. The Kozups' attorney could not be reached for comment.

Matthew Kozup, born on Jan. 10, 1983, received three transfusions on Jan. 12 and Jan. 13 that were contaminated with the AIDS virus.

The blood, which had been donated in October 1982, was supplied to Georgetown by the Red Cross. The donor subsequently developed AIDS and died of opportunistic infections associated with the disease, according to Flannery's decision.

The child died on July 10, 1986, of complications related to AIDS, after spending most of his life in Georgetown and Fairfax hospitals. He weighed only 16 pounds.

In his ruling, Flannery said he was "mindful of the terrible personal tragedy that Matthew's struggle with AIDS must have been for the Kozup family. Theirs is an especially frustrating loss because it was not long after Matthew's infection with the disease that the medical community made a number of important AIDS-related breakthroughs in rapid succession.

"It can only be hoped that these discoveries will save others the pain that {the Kozups} have suffered, and that, toward that end, the efforts of {Georgetown Hospital and the American Red Cross} will play a significant role," Flannery said.