Using steroids to help treat AIDS-related pneumonia could save thousands of lives a year, researchers have found.

Based on five studies, the National Institutes of Health (NIH) formally recommended that AIDS patients suffering pneumocystis carinii pneumonia (PCP) receive prednisone, a steroid. Two of the studies and the NIH consensus report appear in yesterday's New England Journal of Medicine.

"We are not making any claims that this treatment will save money, only lives," J. Allen McCutchun of the University of California at San Diego said in an interview. "And the saving of lives is striking. Steroids offer a big, big benefit for severe PCP cases."

Although drugs are available to prevent and treat the illness, the parasitic pneumonia remains the leading cause of death for people with AIDS in the United States.

Physicians long have reported that severe cases of the pneumonia worsen after hospitalization and treatment with the usual anti-pneumonia drugs and many patients die during that period.

Henry Masur of the National Institute of Allergy and Infectious Diseases found that treatment with trimethoprim or pentamidine kills the pneumonia parasites but also severely inflames cells lining the lungs. Why the inflammation occurs has not been determined, but when it does, cells are unable to absorb oxygen and patients slowly suffocate.

The five studies in the United States and Canada found that prednisone eases the inflammation. The survival rate varies, depending on dosage and how quickly the steroid treatment is begun.

McCutchun's group found that 57 percent of 128 patients treated in standard ways survived, compared with 81 percent of the 123 who were also given prednisone.