PORTLAND, Ore. (AP) _ Seventy-one Pacific Northwest hospitals are tracing the route of 100 pints of blood donated by people who later tested positive for AIDS antibodies, a Red Cross spokeswoman said Thursday.

The suspect blood was donated from 1977 to 1985 by 15 people who returned to give blood after March 1985, when the test became available, said Adelle Martell, spokeswoman for the American Red Cross. None of the donors, all from Oregon, has AIDS.

When the donors were tested, there was no formal program for contacting recipients, said Dr. Frans Peetoom, director of Pacific Northwest Blood Services. Donors were informed that they were at risk for spreading HTLV-III, the virus believed to cause acquired immune deficiency syndrome.

Ms. Martell said there was no way of knowing whether the 15 donors had the AIDS antibody when they donated the blood in question.

''There are probably not 100 people out there with a red X on their foreheads,'' she said. ''It's not AIDS-tainted blood. It's blood that tested positive to the AIDS antibody.''

The presence of AIDS-virus antibodies indicates only that a person has been exposed to the virus; the person may not have the disease.

The Red Cross' Oregon Trail Chapter, which serves 32 counties in Oregon and Washington, has identified the unit numbers of the blood and has asked hospitals to find out who received it.

''We want to find out what happened to recipients,'' Peetoom said. ''If they died we want to know what from. If they are alive we want to know whether they have AIDS or any symptoms, and if they are positive for the antibody we want to counsel them on not transmitting the virus.''

The search for recipients of the blood is being done through a new national program recently instituted by the American Red Cross, the Food and Drug Administration and the national Centers for Disease Control, Peetoom said.

Robert McAlister, program coordinator of the state Health Division's AIDS education program, said that of the 22,173 AIDS cases reported nationally since June 30, 361 adults were infected through blood transfusions and 175 through blood products such as the clotting agent received by hemophiliacs.

AIDS is most often transmitted through sexual contact. In the United States, AIDS has so far been largely confined to male homosexuals, hemophiliacs and intravenous drug abusers.

In Oregon, there have been 93 AIDS cases and 57 deaths reported since 1981, Peetoom said.