The Medicare program has announced a study on whether it would lose money if doctors were told the secret criteria Medicare uses to trigger investigations of whether they are giving patients costly care that is not necessary.

The medical profession, which has been campaigning against "the hassle factor" in the Medicare bureaucracy, believes doctors ought to be told in advance how many treatments are considered excessive so they will have some method of judging what causes their names to pop up in Medicare computers.

Last year, Rep. Fortney H. "Pete" Stark (D-Calif.), chairman of the House Ways and Means subcommittee on Medicare, quipped that telling doctors Medicare's investigative secrets is "like telling the drug dealers when we're going to carry out the raid. The IRS doesn't tell you what the criteria are to trigger an audit."

For years, Medicare has been nabbing potential cheaters by making a computerized review of how often a doctor gives the same Medicare patient a comprehensive consultation, how often he repeats the same treatment, or gives treatments that appear excessive compared to normal practices and may be designed primarily to make more money.

A doctor is flagged by the computer if it discovers that the number of times he is billing Medicare for certain procedures on a given patient exceeds secret internal guidelines used by the various insurance companies that handle Medicare payments to doctors. For example, the computer may discover that a patient is coming in for comprehensive visits so often that it far exceeds anticipated scientific norms.

The computer finding is not considered conclusive evidence, but is only a trigger for a careful medical review of practices to see if there is bilking of the system. "Repeated extensive visits may be medically unnecessary," a Medicare official said.

Some medical analysts have said that disclosing the criteria for such reviews would only allow doctors to increase their treatments up to the known limits but avoid crossing them so they won't be investigated. And that, they said, would result in increased Medicare costs.

The controversy over the review methods produced a congressional mandate for a study to see what would happen if doctors knew the criteria. Secretary of Health and Human Services Louis W. Sullivan recently announced that 13 localities had been selected to participate in a one-year study estimated to cost $400,000.

Medicare Administrator Gail R. Wilensky said the study will involve seven different practices -- nursing facility visits, consultations, hospital visits, comprehensive visits in the office or elsewhere, routine foot care and chiropractic services.

Each insurance company will reveal to doctors in its locale the criteria it uses to flag overutilization on four of the seven criteria. The study will compare practice patterns and billings in the year after the criteria are revealed with those in the preceding year.