HICAGO, March 10 (Reuters) — Clot-busting drugs given to heart attack victims can increase the risk of death, particularly in the oldest patients, a study released today said.

Researchers at Harvard Medical School and Harvard Pilgrim Health Care said the findings suggested that guidelines on the use of drugs like streptokinase should be applied more selectively.

The report, published in the Archives of Internal Medicine, was based on a study of the medical records of 2,659 heart attack patients admitted to 37 Minnesota hospitals from 1992 to 1996. It said 719 of the patients were eligible for the clot- busting drugs according to national guidelines.

The study found that the drugs reduced the risk of death among eligible patients younger than 80 but that patients 80 to 90 years old had an estimated 40 percent greater risk of death compared with patients who did not receive the drug.

Many doctors have been hesitant to prescribe the therapy for the oldest patients, said Steven Soumerai, lead author of the study.

"Our findings, along with those of the earlier study, really seem to justify their concerns," he said.