The Virginia chapter of the American Civil Liberties Union yesterday filed a lawsuit in federal court against the Southside town of Farmville, contending that the town council discriminates against black voters by electing its members at large, rather than by single-member wards.

The lawsuit, filed in U.S. District Court in Richmond, alleges that the at-large system, coupled with the council members' staggered terms, has diluted the voting strength of blacks in Farmville, who number 23 percent of the town's population of 6,067. The lawsuit was brought by the ACLU in behalf of black voters in Farmville.

The black voters contend that because they make up the minority of Farmville's voting population, they cannot elect a black member to the town council under the at-large system. If the town was divided into election wards, the blacks contend they would have a greater chance of electing one or more council members from wards that would be predominantly black.

The suit also names as defendants the board of supervisors of surrounding Prince Edward County, which maintains an at-large system for the three members elected from Farmville. In the late 1950s and 1960s, Prince Edward County came to symbolize Virginia's resistance to integration when it shut down its public schools for four years rather than allow black students to attend with whites.

The Farmville case is the second voting rights discrimination suit brought against a Virginia municipality that relies on an at-large electoral system. The first suit, brought by the Lawyers Committee for Civil Rights against the city of Hopewell, was settled in January 1983 after the city agreed to elect five of its seven city council members in single-member wards.

Last year, the Virginia General Assembly, confronted with pressure from the Justice Department, was forced to adopt a system of single-member legislative districts. The department argued that the state's multimember scheme had discriminated against minorities.

Of Virginia's 41 cities, 33 have at-large electoral systems, a proportion higher than in most other Southern states, said Frank R. Parker, director of the Lawyers Committee's Voting Rights Project. "Virginia hasn't been the subject of attention of civil rights groups, in the way Alabama and Mississippi have," said Parker, who said he expects two or three other voting rights suits to be filed in Virginia this year.

Last week, the Farmville town council rejected a plan to divide the city into seven wards, claiming the proposal was too costly and unnecessary. Town officials had no comment on the ACLU lawsuit.