Federal investigators have issued subpoenas to more than 100 hospitals as part of a nationwide probe into possible Medicare and Medicaid fraud involving the use of unapproved medical devices.

Hospital officials and health care lawyers said Monday that the inspector general of the Department of Health and Human Services has issued the subpoenas to hospitals and some medical equipment manufacturers during the last several weeks. The probe is another sign of the Clinton Administration's aggressive prosecution of health care fraud as part of its efforts to curtail the growth of medical expenditures, hospital officials and lawyers said.

"By the scope, breadth and number of subpoenas people got, the federal government is continuing to focus on health care in a very big way," said Paul DeMuro, a San Francisco lawyer. "They are looking for big-sum recoveries."

In this case, the government is seeking information about a broad array of medical devices used in surgical procedures, many of which involve cardiac catheters and other equipment used in heart surgery, hospital officials and lawyers said. Investigators are examining whether medical devices not approved for marketing by the Food and Drug Administration were used in surgical procedures, or whether FDA-approved devices were used for unauthorized procedures, they said.

The government has not charged any hospital or medical device company with any wrongdoing in the investigation. But if evidence of illegal activities is uncovered, it could mean that hospitals and physicians billed the government for procedures using medical devices that were never proven to be safe or effective.

John Steiner, associate general counsel for the American Hospital Assn., said the subpoenas were sent to as many as 130 hospitals and seek information covering a 10-year period. "We take anything like this very seriously," he said. "The inspector general in the last year or two has settled some very major cases."

Last year, C.R. Bard Inc., a large manufacturer of medical devices, pleaded guilty to criminal charges related to the illegal sale of heart catheters that had not received FDA approval. The company admitted selling the devices without federal approval and illegal testing of the equipment on people.