A 60-year-old tax protester has been sentenced to one year in prison and fined $10,000 for failing to file federal income tax returns in 1976 and 1977, the fourth tax-protest activist in recent years to be convicted in federal court and given prison time in Maryland.

U.S. District Court Chief Judge Frank A. Kaufman imposed the sentence, the maximum on each of two counts, on John L. Sasscer, a Catonsville used car dealer. Kaufman warned a small band of Sasscer supporters in the courtroom yesterday that "people should know that if they disregard the income tax laws, they disregard them at their peril."

Defense attorney Charles Lee Nutt said Sasscer will appeal the conviction. Sasscer will remain free on bond during the appeal.

Sasscer was accused of failing to file returns on gross income of approximately $16,800 in 1976 and $18,150 in 1977.

An activist in an organization called the Free State Constitutionists that claims several hundred members in Maryland, Sasscer ultimately paid the taxes -- about two years late -- but refused to fill out the official government tax return forms that go with the payments.

Prosecutors contended that without the details of his income, deductions and other factors on the form, there was no way to check the reliability of his tax computation.

Sasscer, a heavyset man with an engaging bulldogish face, contended during his trial that disclosure of income and other data on the tax return could subject him to possible criminal investigation in violation of his Fifth Amendment rights against self-incrimination.

He said he had no specific reason to fear an investigation, but there was a potential for it.

Thus, in 1976 and 1977, Sasscer refused to fill out his federal income tax forms, citing the Fifth Amendment and asking the Internal Revenue Service for guidance on what to do. He said he was willing to pay the taxes but did not want to disclose the source or amount of his earnings.

Dissatisfied with the IRS response, he continued to refuse to pay the taxes. After IRS agents visited him in early 1979, he finally made the payments but still did not fill out the tax return.

He said after his sentencing that he has continued to pay his taxes each year in the same manner, although he was indicted only for the years 1976 and 1977.

At his trial, Sasscer cited Supreme Court rulings that he said permitted him to take his Fifth Amendment position.

But prosecutor Elizabeth H. Trimble limited her arguments simply to Sasscer's failure to file the tax returns in 1976 and 1977, and Judge Kaufman instructed the jury that "the taxpayer is not the final arbiter of the Fifth Amendment privilege."

Three other tax protesters have been convicted in federal court here and sentenced to prison since 1981. Recently, 42 members and supporters of the Free State Constitutionists, including Sasscer, also filed a civil suit in federal court challenging the constitutionality of the Maryland state income tax.

At Sasscer's sentencing Tuesday, Kaufman noted that such a civil lawsuit is a proper way to challenge federal or state laws -- "not taking the law into your own hands."