An Arlington Circuit Court judge acquitted Republican Charles G. Viars yesterday of violating a county ordinance by posting large campaign signs during his unsuccessful House of Delegates campaign last fall.

Judge William L. Winston, declining to rule on defense contentions that Viars was a victim of political persecution, granted a defense motion to strike the prosecutor's case.

"This remains where it started -- a simple misdemeanor prosecution," Winston said after a four-hour trial during which three Democratic officeholders testified against Viars. The Republican ran against Democratic Del. Warren G. Stambaugh for the 49th District House seat in South Arlington.

When Viars challenged the sign ordinance in U.S. court last September, the county agreed to apply its law on real estate signs to political signs: They may be no more than 1 1/2 square feet and, unless a permit is granted, can be posted only on weekends.

When Viars allegedly continued to ignore these restrictions, Charlene Bickford, chairman of the Arlington Democratic Committee, brought a misdemeanor complaint against him. Viars was convicted in General District Court in December and given a suspended $25 fine, but he appealed.

Prosecutor Ara Tramblian called several witnesses yesterday, including several zoning inspectors, who testified they had removed dozens of Viars signs from public lands, some of which were 4 square feet and all of which were posted after the agreement on sign sizes. Also called were County Treasurer Frank O'Leary and his chief deputy, Kevin Appel, both Democrats, who said they, too, had removed some of the signs.

Dorothy Stambaugh, a Democratic appointee to the School Board and wife of Viars' campaign opponent, was the only witness who said she saw Viars putting up a large sign and loading others into his car.

Winston agreed with defense attorneys Louis Koutoulakos and John Snider that there had been no evidence that Viars or his campaign staff had erected signs on Oct. 29, the date cited in the charge. Koutoulakos called the charges "a real petty case . . . garbage" and said Viars was a victim of "political persecution."