In April, 1865, Union troops seized this city in what proved to be the last great battle of the Civil War. Today, more than a century later, blacks are invoking the Voting Rights Act in asking the federal government to intervene again in a bloodless but bitter struggle for control of a historically rich but economically decaying community.

The second battle of Petersburg, Virginia's most predominately black city, is over redistricting of the city's seven wards. Whites, who hold four of the city's seven council seats depite the fact Petersburg is 61 percent black, recently redrew the lines in a way that blacks claim guarantees white domination for the next decade.

There is nothing polite about this dispute, which has destroyed most semblances of racial harmony in this city of 41,000 and and turned council meetings into vicious and at times race-baiting affairs. The white mayor, who called a black councilman "boy" at one recent meeting, says he is attempting to prevent this Southside Virginia community from becoming "a welfare city." His son-in-law, whom the mayor appointed to the city school board, suggested at another session that residents of public housing projects are "parasites."

Blacks, in turn, have labeled the mayor a racist and charged that he and other whites on council are out to enrich themselves and their cronies at the expense of the poor.

"This is a classic example of why there is a need for the Voting Rights Act," says Councilman Hermanze E. Fauntleroy Jr., a black leader who, along with the American Civil Liberties Union, is asking the Justice Department to throw out the redistricting plan as a violation of the act. "Without it, we just wouldn't have any way to redress this problem."

At stake is more than who sits on the council. Mayor LeRoy B. Roper, architect of the redistricting plan, also has led drives that killed a new public housing project financed solely by federal money, and denied increased city funds to Petersburg's 80-percent black school system for the past three years.

Roper, who denies any racial motives to his actions, says that he also would like to see cutbacks in welfare programs and the elimination of Legal Aid.

"We've got to stop being a welfare city that attracts welfare people from outside the city," he says. "To survive, we need to bring back the moderate and high-income people we lost."

Blacks, who are on the opposing side on these issues, say that Roper's statements are filled with racial code words. "He's really talking about maintaining white supremacy in this city," says Fauntleroy. They also charge that Roper and Vice Mayor Charles H. Cuthbert oppose Legal Aid because they and their friends own slum housing whose tenants rely on Legal Aid lawyers for protection, an allegation that the mayor denies.

About the only thing both sides agree on is that Petersburg, gateway to Virginia's rural Southside 125 miles south of Washington, is in trouble economically. The city, whose skyline largely resembles the one Union Gen. Ulysees S. Grant saw from the bluffs to the east of town in 116 years ago, has shown little job growth in the last decade. The city's property tax rate of $1.65 per $100 of assessed value is one of the highest in Virginia.

The city gained about 5,000 in population during the past decade, but Roper says that most of the new arrivals are poor blacks from the rural South who are on welfare. The mayor says his most telling statistic is that of the last 32 employes moved to this area by Brown & Williamson Tobacco Co., the city's largest manufacturer, 31 chose to live outside of town.

More than 800 families are on waiting lists for public housing, while last year the city actually had a net loss in housing units. "We've knocked more houses down than we've put up," says Councilman Joseph M. Schein.

For decades, this city was run by a small group of white businessmen and bankers, most of whom had homes in the exclusive Walnut Hill area and bloodlines that dated back several generations.

"It was our own little version of the Byrd Machine," says Florence S. Farley, a psychology professor who is one of the most outspoken of the black councilmembers.

Blacks, aided by the Voting Rights Act, altered the balance of power here a decade ago. When white city fathers, faced with a majority black population, annexed enough neighboring suburbs to add 8,000 new white residents, blacks went to court, charging that their voting strength illegally had been diluted. A federal judge, citing the act, agreed and ordered the city carved into wards, to give blacks a fair chance to capture control of the council.

They did just that in an interim election in 1973, winning four of the seven seats and naming Fauntleroy mayor. Whites returned to power the following year, but for a while it looked as though a biracial coalition would rule the city. Fauntleroy was renamed mayor by a council dominated by whites.

By last year, however, racial lines had hardened again. Two white councilmen, Schein and John W. Slate, who often had allied themselves with the blacks, voted instead with their two white colleagues to oust Fauntleroy and name Roper as mayor. Blacks claime that the two sold out under pressure from the white community. Schein indicates that they were alienated by the increasingly vocal militancy of black council members, especially Farley.

Whatever the reason, when it came time to redraw ward boundaries this fall, the whites united behind a plan that some privately concede was aimed at ousting Farley.

The plan, passed earlier this month at a raucous council session, eliminates about 1,500 blacks from Farley's ward by cutting off its western side and dipping south to add nearly 1,200 whites from the annexed area. It reduces blacks to61 percent of the population in Farley's ward and in another where they previously had been around 70 percent. Given the fact that the black population includes more children and less registered adults, opponents say that white voters are likely to dominate both wards.

"There's no doubt that the idea was to dilute the black vote and get rid of Mrs. Farley," says Chan Kendrick of the Virginia ACLU, who contends that the plan will produce a 5-to-2 white majority on the city council.

The council now has to submit the plan to the Department of Justice, which under the Voting Rights Act must determine whether the redistricting will have an adverse impact on black voting strength. Should Justice approve the plan, the blacks say they are prepared to challenge it in federal court.

"The bottom line is: Roper's people left this city, while we elected to stay," says Farley. "Now why is it that he should still control our destiny?"

The white council members, pointing out that Vice Mayor Cuthbert won his seat last year in a71 percent black ward, say blacks are trying to gain from federal intervention what they failed to win at the ballot box.

"It angers me to have the Justice Department looking over our shoulder," says Schein, who adds that the blacks "can yell racism all day long, but all I'm trying to do is what's best for the city."

Others outside the of fray say that the increasingly vituperative attacks from both factions are harming Petersburg by frightening off new business.

"Both sides believe their values are best for the city," says Father Thomas Long of St. Joseph's Catholic Church, the city's only fully integrated church. "But they're fighting like cats and dogs and the trouble is, they're not the only ones getting scratched."