A Queens drug rehabilitation clinic was fined $16.5 million for cheating the state’s Medicaid system, Governor Pataki’s office said yesterday. The fine is the biggest ever by the state Medicaid Inspector General and the Office of Alcoholism and Substance Abuse Services.

Mr. Pataki’s office also said it was stopping another $30 million in payments to Community Related Services Inc.,a provider of outpatient treatment.

The state charged the business with more than 45 regulatory violations and 25 cases of Medicaid fraud, waste and abuse over a number of years. OASAS will revoke the clinic’s operating certificate.

Fraud in the state’s $44.5 billion health care program for the poor costs taxpayers perhaps billions of dollars a year, according to state officials, though the state has no reliable estimate.

Investigators found CRS patients on average made 152 visits to the clinic a year, compared with the average 34.4 visits for patients going to other clinics in the OASAS system. Many of the patients “have seemingly not had abuse or dependence issues for years,” Mr. Pataki’s office said.

CRS patients tended to stay in the clinic for more than 20 months on average. The statewide average length of treatment is 3.7 months.

The clinic was targeted after a computer search picked up suspicious Medicaid billing patterns.

“CRS was cheating the state’s Medicaid program at the expense of patient care — an abhorrent practice — and a practice that will come to an end thanks to this enforcement action,” Mr. Pataki said.

Clinic managers did not return a call for comment.

In June, a federal review concluded that the Pataki administration has not done enough to fight Medicaid fraud and waste, with too many staff cuts and too little enforcement.

Responsibility for policing Medicaid is shared by the state Department of Health and the attorney general’s office.

State officials said the reviewers overemphasized specific parts of their program but lost sight of the big picture, which they said shows significant improvement.