Virginia gubernatorial candidate Charles S. Robb was accused today of securing the support of the state's foremost black political organization by funneling the group money in advance of its expected endorsement of Robb and his Democratic running mates.

The charge by three black independents who are staging what they concede will be a futile write-in campaign for the state's top political offices, was immediately denied by the Robb campaign and the chairman of the Virginia Crusade for Voters.

The exchange, on the eve of the Crusade's endorsement meeting here, underscored the deep and increasingly bitter split in the state's traditionally Democratic black community over the conservative Robb.

Cora Tucker, a Halifax housewife running as a write-in gubernatorial candidate, accused the Crusade and other black organizations supporting Robb of "falling for conniving promises made to their leaders." She labeled Robb and his Republican opponent, J. Marshall Coleman, as "Tweedle Dee and Tweedle Dum, Virginia's political twins," and accused them of courting white conservatives while ignoring black interests.

Her running mate for attorney general, James Ghee, a member of the Prince Edward County Board of Supervisors, said at a press conference the Robb campaign had already donated "in the neighborhood of $25,000 to $30,000" to the Crusade in return for tomorrow's endorsement. Ghee, who refused to name the source of his information, charged that the Crusade "has been bought before the decision is made."

Ghee refused to characterize the donation as illegal. "Draw your own conclusions," he told reporters at the State Capitol.

William S. Thornton, the Crusade's chairman and a Richmond podiatrist, called Ghee's accusation "an attempt by an ambitious person to tarnish our credibility . . . We have not asked for any money and we have not received any money. We do not even have a treasurer."

"Street money" is a traditional element in Virginia election campaigns and candidates in the past have spent $50,000 to $75,000 to turn out black voters, who make up an estimated 13 percent of the state's registered voters.

Thornton said the Richmond Crusade for Voters, a separate organization from the state Crusade, traditionally has received $8,000 to $12,000 from candidates it endorses. The money, he said, is used to pay for posters, brochures and the "guide ballots" that the vast majority of urban blacks are said to use at the polls. The funds are also used to pay poll workers in black precincts on election day.

The Richmond Crusade and its sister group, Concerned Citizens in Norfolk, are expected to back Robb. Robb spokesman George Stoddart said the campaign has not donated money to any black group, although he left open the possibility that funds would be made available once the endorsements had been made.

Blacks from Southside Virginia's 5th Congressional District launched the write-in effort a month ago after complaining about a lack of responsiveness from Robb and Coleman, both of whom had received considerable black support four years ago in their contests for lieutenant governor and attorney general.

Many blacks have been upset with Robb's refusal to support extension of the key "preclearance" provision of the Voting Rights Act, a major civil rights measure originally passed under the leadership of Robb's late father-in-law, President Lyndon Johnson. The provision requires states such as Virginia with a history of racial discrimination in voting to secure prior approval from the Justice Department for all election law changes.

In recent weeks, Robb has softened his position, saying he would support extension so long as an amendment was added allowing states and localities with a clean record to eventually escape federal oversight. He has added that Virginia would not be eligible for such a "bail out" because of the department's recent finding that the state's legislative reapportionment plans were discriminatory.

That change has not been good enough for many blacks. On Wednesday, Robb was castigated by NAACP leaders in Alexandria for his voting rights stand as well as for his support of the Reagan administration's federal budget cuts.

At their press conference today, the black write-in candidates labeled Robb's change "political crumbs," which Tucker said were too little and too late to persuade them to call off their campaign.

The write-in effort has not attracted much support statewide. Even as they attacked Robb, Alexandria black leaders conceded they would probably support his election and recent polls indicate Robb can expect to receive up to 90 percent of the vote from blacks who, while dissatisfied with him are even more concerned about Coleman's close identification with President Reagan.

"Chuck's not all I would like in a candidate but I do recognize the fact that this is Virginia," said Newport News Del. Robert C. Scott, one of only five blacks in the 140-member General Assembly. Scott said the Crusade would endorse Robb because "What other choice is there?"

Still, some Robb aides privately concede the write-in campaign could cost their man between 5,000 and 10,000 normally Democratic votes, enough to hurt him in a close race. Equally important, they fear it could be a factor in causing other blacks and white liberals to stay home on election day. Robb himself has called the black vote "the critical margin of difference" that could determine this year's winner.

The write-in candidates deny their movement is aimed at either candidate, although their candidate for lieutenant governor, Lynchburg accountant Jesse Jeffress, attended the Republican National Convention last year as an alternate delegate pledged to Reagan. That has led to suggestions from some Democrats that Republicans are backing the write-in effort, a charge that the Coleman campaign denies.