BALTIMORE, DEC. 13 -- Iran-contra figure Thomas G. Clines, convicted in September of filing false income tax returns, was sentenced today to 16 months in prison, the stiffest imprisonment imposed on any of the eight convicted Iran-contra defendants.

U.S. District Judge Norman P. Ramsey also fined Clines $40,000 and ordered him to pay the costs of prosecution by the office of independent counsel Lawrence E. Walsh.

In a statement, Walsh said, "We very much appreciate Judge Ramsey's fair and efficient handling of the entire prosecution." Prosecutor Stuart A. Abrams of the independent counsel's office said he was "gratified" with the sentence.

Clines, who was ordered to report to prison in 45 days, is free on bond while his attorney, Paula Junghans, prepares an appeal.

Clines, 62, a former Central Intelligence Agency agent and member of a secret White House network that sold arms to Nicaraguan rebels when such sales were outlawed by Congress, was convicted Sept. 18 of failing to disclose $260,000 in arms sales profits on his income tax returns and failing to file reports on foreign financial accounts in 1985 and 1986.

The network also sold arms to Iran in exchange for Americans held hostage in the Middle East and used the profits to buy arms for the contras.

A key figure in the scandal along with former White House aide Oliver L. North, Clines used "sham corporations and Swiss bank accounts" to enrich himself, Abrams said. "This was not a case of misplaced patriotism," he said. "It was purely a case of greed."

Abrams renewed a complaint that Clines, in an effort to understate his financial condition and avoid heavy fines at sentencing, transferred to "nominees" several pieces of real estate worth hundreds of thousands of dollars while maintaining control of them.

Junghans countered that title records show Clines did not own the properties and that they were properly transferred.

In asking for leniency, Clines told Ramsey, "My country, my family and my reputation mean everything to me." He said he had dedicated 40 years to public service, much of it in the CIA, "risking my life many times."

Until today, former national security adviser John M. Poindexter, who is free pending an appeal of his conviction on five felony counts, had received the only Iran-contra prison sentence -- six months.