An Annapolis man who claimed he was eligible for more than $300,000 in charitable contributions on his federal income tax returns for a fishing vessel he bought for $70,000 was convicted yesterday in U.S. District Court here of six income tax violations.

Robert B. Wilhelm III, 56, who lives in Annapolis and is a manager of the Robert B. Wilhelm Funeral Home in Suitland, was found guilty after a week-long trial of evading as much as $100,000 in taxes for 1980, 1981 and 1982.

The jury deliberated about six hours over two days before reaching its verdict on the three income tax evasion charges and the three counts of making false statements on his tax returns.

U.S. District Judge Norma H. Johnson required Wilhelm to post $50,000 in securities to remain free until his sentencing.

He could be sentenced to up to 24 years in prison and a $1.5 million fine.

The case against Wilhelm, which was prosecuted by Assistant U.S. Attorney Mark H. Dubester, revolved around the 65-foot fishing boat, Katherine E, that Wilhelm purchased in 1972 for $70,000. In 1980, Wilhelm tried to give it to a Forestville church, which turned down the gift, and the boat remained docked on Wilhelm's property in Ocean City.

Later that year, according to testimony, Wilhelm tried unsuccessfully to sell the boat, and he then gave it to an individual in 1981. That person later sold the boat for $10,000, and Wilhelm eventually signed the title over to him.

But on his 1980 tax returns, Wilhelm claimed he was eligible for a $327,000 charitable deduction.

Because such deductions are limited to a percentage of gross income, Wilhelm was able to carry forward the deduction onto his Internal Revenue Service forms for 1981 and 1982.

Internal Revenue Service officials estimated that by using the scheme, Wilhelm evaded paying between $85,000 and $100,000 in taxes.