"Project Integrity," a Carter administration search for the "most outrageous" cases of Medicaid fraud by doctors and druggists, has turned up 537 "verified" cases so far, Health, Education and Welfare Secretary Joseph A. Califano Jr. reported today.

New ones are being added daily, he said, in what seems to be the most determined attempt by an administration to curb cheating on healthcare bills.

The 537 cases - 315 representing apparent violations by doctors, 222 involving druggists - include 172 first reported by Califano nine days ago.

Many state governments are cooperating, and 2,000 more names have been sent to the State of California alone to check, Califano added. The FBI is assisting in investigations.

A similar search is being started on a far larger number of Medicare payments, he told a news conference.

Medicare is the federal program to pay medical bills for the aged and disabled. Medicaid is a federal-state program to pay medical bills for low-income people.

The Medicaid search is expectdd to turn up "at least 1,000 of the most hard-core, the very worst cases," even before the far larger Medicare investigation is completed, other HEW sources said.

This could mean that federal attorneys will soon face the task of screening thousands of apparent fraud cases for possible prosecution.

"In some cases, I'm sure there will be prosecution," Califano said. In others, money will be recovered, he predicted, by civil suits, if necessary.

"The difficulty in prosecuting these cases means you have to go after the most flagrant ones," another HEW official commented. Programmed to pick out only the most serious apparent violations, the computers turn up many that seem to be fraud, yet might not be proved in court or before a jury trying to weigh a doctor's "judgment."

Califano appeared after examining the San Francisco headquarters of the big West Coast nonprofit Kaiser Foundation pre-paid health plan.

On Sunday, he will address the House of Delegates of the American Medical Association, which he criticized earlier this spring for trying to block the administration's hospital cost controls.

AMA officials said they welcome the federal antifraud effort and promised increased medical efforts, against cheaters and unfit and incompetent doctors.

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Califano called the overwhelming number of physicians and pharmacists honest aid dedicated.

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Califano praised the Kaiser Health Plan - which gives total care for a set monthly sum - for delivering high quality care far more cheaply than the usual fee-for-service system. He said the Carter administration will push this "Health Maintenance Organization "coucept, started by President Nixon, and will continue pushing Congress to put a lid on hospital costs.