PORTLAND – The top executive of the former Jackson Brook Institute has agreed to plead guilty to filing a false tax return and to making false statements concerning Medicare and Medicaid payments to the facility.

Frederick Thacher of Boston faces up to four years in prison and a fine of $350,000, U.S. Attorney General Paula Silsby said Monday.

Medicare and Medicaid programs paid excessive sums to Jackson Brook as a result of Thacher’s failure to disclose he had received $350,000 in consulting fees from the company that provided physician services to Jackson Brook, Silsby said.

Thacher also violated federal tax laws by failing to declare his consulting fees as income, she said.

Thacher was formerly the chairman and chief executive of Jackson Brook, which was the state’s largest private psychiatric hospital when it went bankrupt and was sold in 1999. The South Portland facility is now called Spring Harbor Hospital.

Federal investigators first started examining Thacher after he was questioned about the consulting income during Jackson Brook’s bankruptcy proceedings.

If Thacher had disclosed his consulting fees, then the hospital and the physician group would have been classified as “related parties” and the hospital would have received significantly less Medicare and Medicaid funding, Silsby said.

“When a corporation or corporate executive defrauds our nation’s health care programs, scarce resources are diverted away from patient care and money is taken out of the pockets of American taxpayers,” Silsby said.

Peter DeTroy, a Portland attorney who represents Thacher, said he expects his client to be sentenced before the end of the year.

“He’s glad to put this behind him,” DeTroy said.