WHITE PLAINS — A former state senator was sentenced in federal district court here on Friday to 21 months in prison and three years of supervised release after pleading guilty last year to obstruction of justice and tax evasion.

The former senator, Vincent L. Leibell III, a Republican from Putnam County, had faced 18 to 24 months in prison, based on sentencing guidelines. But Mr. Leibell’s lawyer, David L. Lewis, asked the judge to take into account Mr. Leibell’s “life of public service” and urged him to consider a “non-guideline” sentence, like allowing Mr. Leibell, 64, to do community service, “in which he publicly has to restore the faith in the people he has betrayed.”

“We don’t have public stocks anymore, where he can stand with his head and arms in stocks,” Mr. Lewis said, trying to convince the judge that Mr. Leibell’s crime would be forgotten in jail, but that doing some sort of “social restitution” would be more humiliating for Mr. Leibell and would offer a broader, more public lesson.