The black majority of the Richmond City Council was on the verge of firing its white city manager last night in the climax of a simmering drama that has shocked the city's white business leaders and demonstrated with finality that political power in the old Confederate capital has shifted from white to black politicians.

With a boldness that eventually eroded some of his support, City Manager William J. Leidinger has been fighting his impending dismissal for a month. The public campaign to save him raised the specter that his firing would halt downtown redevelopment and even undermine the city's credit ratings.

Since a black council majority was first elected in March, 1977, there has been a growing debate over whether the city emphasizes commercial redevelopment at the expense of social programs. About 45 percent of the city's population is black, but until last year black office-holders were in a small minority unable to challenge the influence of the white business leadership.

The debate evolved into a confrontation between the black council majority and the white manager that has become the most explicit racial conflict in Richmond since desegregation of the city's schools in the 1960s.

Repeated suggestions that the firing is a "racist" act have been heatedly denied by Mayor Henry L. Marsh III, one of the state's most prominent black civil rights advocates both as a lawyer and a political figure.

The council met to consider Leidinger's dismissal in a quasi-judicial hearing in a council chamber packed with 400 spectators.

A formal statement charging Leidinger with "lack of respect" for the council's policy-making role was read to him. He was charged with neglect of minority hiring, delay of neighborhood renewal projects, "obsessive" attention to downtown commercial developments and consistent underestimation of city revenues.

With the aid of two lawyers from one of Richmond's largest law firms, Leidinger denied all of the charges in detail. He said, for instance, that the percentage of minority city employes is almost identical to the minority ratio in the Richmond population. He added that 45 percent of the 18 department heads and assistant city managers he has hired during his six-year tenure have been nonwhite.

Leidinger disclaimed responsibility for the public controversy over his proposed firing. He said, however, that after he was told by Marsh on Aug. 1 that the black majority wanted him to go, he consulted with friends and decided, "I could not work this out in a quiet manner."

Council member Wayland W. Rennie, who is white, said in an interview before the hearing that he saw no chance that the manager's defense would sway any of the five council votes publicly committed to his dismissal.

Speaking of the mayor, Rennie said, "He has those votes right under his thumb."

The charge that racism is behind the firing was given a measure of credibility yesterday in a final, bizarre twist to what has become known here as the "Leidinger affair."

W. H. C. Venable, a white lawyer who conducted the seven-year legal battle that led to black control of the City Council, sent a letter to Marsh and other council members chastising them for the way they have handled the manager's firing.

As quoted at length in yesterday's editions of the Richmond Times-Dispatch, Venable reminded Marsh in the letter of private conversations over the last 18 months in which the mayor disclosed his desire to get rid of the manager and City Attorney Conrad D. Mattox Jr., who also is white.

In one of those conversations, Venable was quoted as saying in the letter, Marsh referred to Leidinger as a "honky."

Marsh denied Venable's charge, saying in a prepared statement, "Mr. Venable's statement is a vicious lie and is part of a desperate campaign by a group of desperate men to discredit the black members of the City Council. I never called anybody a 'honky.'"

Nevertheless, Venable's letter had a dramatic effect, because in a city of historically polarized races he has been conspicuously associated with the drive for a full political role for the black population.

When in 1970 it appeared that black voters would soon make up the majority of the city electorate, the white-majority council annexed a predominantly white, 23-square mile area from neighboring Chesterfield Country. Venable, representing black civil rights activist Curtis Holt Sr., challenged the annexation as a ruse to dilute black voting power.

"Federal courts finally allowed the annexation, but required the city to adopt a nine-ward system that produced a black majority of five on the council in a 1977 special election. Marsh was elected mayor by the new majority, which was continued in a regular election this year.

In the first 18 months of black majority rule, there was conspicuous cooperation between the new black officeholders and the city's conservative business establishment. By running a council slate under the banner "Team of Progress" and playing a heavy role in selection of past managers, that business establishment has historically dominated Richmond politics and government.

Marsh has said that the appearance that white business influence has continued under the new council has resulted in criticism of the black council members by many of their supporters. The feeling of some blacks that business leaders do not respect the new council majority was recently expressed by one of its members, Claudette B. McDaniel.

"They're looking at us like they look at their housekeepers, like we don't know what we're doing and can't take care fo business," she was quoted as saying during the Leidinger controversy. "They're not used to dealing with black people on their level."

Leidinger, 38, came to Richmond as assistant city manager in 1971 and was elevated to manager a year later. Before coming to Richmond, he had been assistant city manager in Alexandria.

The resolution proposing his dismissal would make it effective Oct. 6. Leidinger has said that he probably will seek a job in private industry after leaving the city government.