Mr. Bruno, 80, is scheduled to be sentenced on March 31 and faces up to 20 years and a $250,000 fine on each felony count. But Judge Gary L. Sharpe has broad discretion in sentencing, and Mr. Bruno’s defense was expected to appeal.

“I am very, very disappointed in the verdict,” Mr. Bruno told reporters on the steps of the federal courthouse here. “The legal process is going to continue. In my mind and in my heart, it is not over until it’s over. And I think it’s far from over. Thank you all, have a good night and merry Christmas.”

The jury entered the courtroom at 4:16 p.m. and as the verdict on first counts were revealed  not guilty on the first and second, no verdict reached on the third  the mood among Bruno supporters in the courtroom grew almost euphoric.

But as Judge Sharpe read out a guilty verdict on the fourth count, the mood turned. Mr. Bruno’s normally upright frame sagged. “We established at this trial that Bruno exploited his office by concealing the nature and source of substantial payments that he received from parties that benefited from his official actions,” Andrew T. Baxter, the acting United States attorney for the Northern District of New York, said in a statement.

The federal statute under which Mr. Bruno was charged, which makes it a crime for officials to use wires or the mail to deprive constituents of their “honest services” by concealing conflicts of interest, are set to be reviewed by the Supreme Court and could be struck down in whole or in part during the coming months, potentially aiding any appeal.