A political power play by a group of white business leaders is threatening to topple one of Virginia's leading black elected officials, Mayor Henry L. Marsh III, and end six years of black control in this former Confederate capital.

The threat to Marsh comes at a time when the 48-year-old veteran civil rights lawyer has been receiving increasing national attention as an outspoken critic of Reagan administration urban policies. At the U.S. Conference of Mayors meeting recently in Minneapolis, Marsh led the attack on an administration draft plan as a "declaration of war" on the cities.

Marsh has also been recently courted by all the major Democratic presidential hopefuls. After he won easy reelection to his City Council seat here last month, for example, Marsh received congratulatory phone calls from former vice president Walter Mondale and Sen. Edward M. Kennedy (D-Mass).

Yet Marsh's stature in the big leagues of Democratic urban politics is not helping much in his own backyard. A newly elected black City Council member named Roy A. West has kept the city in suspense for weeks by hinting that he will line up with the four whites on the nine-member council and vote to unseat Marsh as mayor at a meeting scheduled for Thursday.

Behind the scenes, the oust-Marsh campaign is being orchestrated by the mayor's longtime enemies on Main Street -- the central Richmond thoroughfare that is the seat of the town's almost exclusively white business establishment. During a series of private meetings with Main Street leaders during the past month, West--a middle school principal who has never before held elected office--has even been offered the mayor's job himself if he will team up with the white members of the council in deposing Marsh.

"This is historically the way whites have sought to maintain political control--by dividing the black community," Marsh said in an interview in his law office last week.

"We've made inroads in the white community with our efforts to cooperate," he adds. "But the hard-core opposition is still there . . . There's still a resentment over the fact that blacks provide the leadership in this city."

The mayor's critics, though, insist that it is he who has fanned the flames of racial tension through a confrontational brand of politics that has produced endless bickering with white council members. The whites complain that Marsh's imperious executive style has virtually frozen them out of City Hall decision making.

"There's 99 percent lack of communication between the mayor and me," grouses Stevenson Kemp, a white council member and self-styled Ronald Reagan Republican. "He just runs the city as he pleases. It's King Henry."

"As far as I'm concerned, Henry Marsh has had his chance to run this city and the result has been chaos in terms of race relations," adds Henry Valentine, a Main Street stockbroker, Republican party fund-raiser and former vice mayor.

Valentine, along with Main Street doyen J.C. Wheat, has been one of the business leaders behind the effort to recruit West as the new mayor, a post that is elected by the council. "I've told him West that he could do exactly what he wants to do as mayor--just so long as he treats my people with an open mind," says Valentine.

Richmond's latest travails, and the undeniable racial tensions that lie beneath them, suggest both the possibilities and limits of the newly extended Voting Rights Act--a pivotal force in the city's recent history. Blacks, who now make up 51 percent of Richmond's 219,000 population, first won control of the City Council here, and elected Marsh as mayor, after the Justice Department used the law to strike down the city's old at-large voting system and institute a ward system that better reflected black voting strength.

Ever since, blacks have reigned at City Hall, but patterns of segregation persist on Main Street. Richmond, with its wealth of corporate headquarters, has long been considered a major business capital of the South. Yet a new study by two sociologists at Virginia Commonwealth University found that, of 1,532 corporate officers, board members and executives based here, only nine are black.

As the seat of the 4th U.S. Circuit Court of Appeals, it is a southern legal capital as well. Yet not one of the town's 50 largest law firms has a black partner, according to the study.

"For many years to come--if not forever--the whites are going to dominate the economic structure here," Marsh says.

Richmond has been buffeted by the same forces that have hit other urban areas. White flight to the suburbs and a recessionary economy have shrunk the city's tax base, while Reagan budget cuts have decimated its social services. Although the city managed to finish its fiscal year with a $8 million surplus, it was only through painful budget pruning that nearly wiped out its child day-care and senior citizen programs, shut down recreation centers, and eliminated more than 100 welfare department jobs. "We're just holding on by our fingertips and hoping something turns up," says Larry Hughes, Richmond's budget director.

The Reagan era also has seen a retreat from one of the hallmarks of Marsh's tenure--a series of highly publicized federal grants that were chalked up to the mayor's ties to the Carter administration. Marsh had been one of the earliest Virginia supporters of Carter during the 1976 campaign, a political move that paid off handsomely after he took office.

Embraced by the Democratic administration as a leading black urban spokesman, Marsh became a frequent guest at White House dinners and Kennedy Center ballets and other Washington events. The benefits to the city came through such awards as two multimillion dollar grants for the renovation of the Jefferson Hotel on Franklin Street and the conversion of the Main Street Train Station, a turn-of-the-century Victorian landmark, into a Georgetown Park-like shopping center.

Today, says budget director Hughes, both projects are dead, victims of ruinous interest rates and federal budget reductions.

The cutbacks notwithstanding, the chief complaint against Marsh revolves around his repeated squabbling with the white minority on the council. The bickering dates back almost to the day he took office in 1977. Aided by the new black majority on the council, Marsh quickly began transforming the largely ceremonial and part-time mayor's post into a political power base. Expense accounts were instituted, salaries were raised and the white city manager was fired--all over the heated objections of the white minority.

Buford Scott, the city's new Chamber of Commerce president and a leading Main Street moderate who supports the mayor, says Marsh's behavior can be understood, if not condoned, by history. "For many years, Henry Marsh was the black leader who had more reason to be frustrated than any other because he was on the council when the white majority was not paying any attention to what he had to say," he says. "Now that he's in power, Henry has understandably decided that his time had come."

Thursday, however, it will be up to West to decide if Marsh's time is over. The new black council member has refused to say how he will vote, but noted that he has been bombarded by phone calls urging him to accept the whites' offer and take the mayor's job. "There's an awful lot of desire for change out there," he said. "I think there's a feeling that maybe we need a clean sweep at the top."