BANGOR, Maine — A local chiropractor pleaded guilty Monday in U.S. District Court to tax evasion one week before his jury trial was scheduled to begin.

Dr. Richard J. Thomas, 64, who operates the Thomas Wellness Center on Stillwater Avenue, was indicted more than three years ago on six counts — one for each year — of tax evasion between 1995 and 2001.

In a plea agreement with prosecutors, Thomas admitted Monday to evading paying federal income taxes in 2001. The counts covering the previous years are expected to be dropped after the chiropractor is sentenced.

Thomas also agreed to waive his right to appeal the sentence if it does not exceed 18 months.

The chiropractor could be ordered to pay back taxes for all six years. Assistant U.S. Attorney James McCarthy estimated Monday that Thomas owed between $200,000 and $400,000 in back taxes.

Thomas is free to dispute that figure at his sentencing hearing, U.S. District Court Judge John Woodcock told him Monday.

A sentencing date has not been set. He remains free on personal recognizance bail.

In pleading guilty, Thomas conceded that the government would be able to prove he did not have a “good faith basis” for refusing to file federal tax returns or pay taxes. In addition, the chiropractor admitted using a number of deceptive techniques to attempt to dupe the government, according to court documents.

Among them was establishing in August 2001 a Nevada corporation called Three Crows to hide assets, Thomas admitted Monday. He got a credit card and deposited business receipts under its name.

Thomas also transferred real estate and registered a boat he had bought with cash under the names of two separate trusts, according to court documents. He also allegedly used cashier’s checks to conceal personal expenses and withdrew large sums of cash from his bank accounts to misrepresent his income and assets, McCarthy told Woodcock on Monday.

Virginia Villa, the federal public defender based in Bangor, has represented Thomas since May, according to court documents. Thomas, however, represented himself before he was indicted by a federal grand jury in January 2006.

Acting as his own attorney before that, Thomas sought in 2002 to quash demands by the Internal Revenue Service for financial information from banks, credit card companies and other financial institutions he had done business with. Thomas lost that case two years later after he appealed it himself to the 1st Circuit Court of Appeals in Boston.

The chiropractor is not facing similar charges in state court, according to the Maine Attorney General’s Office that is responsible for investigating and prosecuting cases of evading the payment of state income taxes.