It's called the Flamingo Club, a combination restaurant, social club and all-purpose meeting hall on a battered commercial strip in this city's black North Side. Last week its basement was the scene of the shortest gubernatorial endorsement meeting that the Richmond Crusade for Voters has ever held.

In less than five minutes the Crusade, the city's dominant black political organization, endorsed Charles S. Robb and the entire Democratic ticket. There was no discussion and no dissent.

How has Robb, an avowed conservative, won such strong support among Virginia's black voters? His secret weapon: Ronald Reagan.

More than anything else, it is fear of the Republican president and distrust of his programs that seem to be motivating black voters to give Robb their overwhelming endorsement. Interviews with black voters in Richmond and Norfolk, the state's largest black communities, found virtually no support for Republican J. Marshall Coleman but strong support for Robb.

That contrasts to four years ago when Coleman, running for Virginia attorney general as a progressive Republican, surprised a lot of people by capturing the backing of the Crusade over a conservative Democrat. Coleman went on to win, by one expert's estimate, about 55 percent of Richmond's black vote and 32 percent of black voters statewide.

This year, running against Robb, who is also considered a conservative Democrat, Coleman will do well to get more than 10 percent, according to analysts and polls. Robb, who is predicting a close election, says the degree of support he receives from blacks will make "the critical margin of difference" to his race.

Blacks make up about 14 percent of the state's registered voters, but traditionally they compose only 9 to 10 percent of actual voters in state elections. That could be enough to be the deciding factor in a race that is as close as this year's race for governor.

The Coleman campaign has sought since the beginning to make this year's Virginia election a referendum on Reagan, who polls show is overwhelmingly popular in this conservative bellwether. Black voters, at least, seem to be buying the idea but their reaction is almost uniformly negative.

"I was a Coleman fan but as it got to election time and he was aligning himself so closely to Reagan, I had to let him go," said Tyrone Gaines, a state data-processing worker here, who says he voted for Coleman four years ago and for John Anderson in the 1980 residential race. "This time it's more of a referendum on Ronald Reagan and because of that, I've got to go with the Democrat."

Said Victor Everett, a Norfolk store clerk: "We don't need any more Republicans. Ronald Reagan is enough. Ronald Reagan and Coleman, they would try to burn us."

Some say they oppose Reagan's social welfare cuts because they see its impact on neighbors. For others, the cuts have had a more personal impact. Donna Carter, a Richmond social worker, says she was recently demoted and lost $3,000 in annual salary after her department was reduced. She cites that as partial explanation of why she is for Robb.

Still others say they agree with the president that welfare programs need stricter regulations, but can't fathom the rationale behind other cutbacks.

"We need a shakeup of welfare," said Larry Hall, a Virginia Electric and Power Co. meter reader who cites a neighbor, a welfare recipient who Hall says can afford the monthly mortgage on a $70,000 house. Hall can't accept federally mandated cuts in school lunches and federal aid to education.

"Why should the kids have to suffer?" he said. "Reagan should cut defense instead. He's setting us back 20 years."

Robb, who says he supports most of the Reagan budget reductions, would appear to have little to offer people stunned by the president's policies. Until a few months ago, he opposed a critical provision of the Voting Rights Act, a stand he now seems to have softened. Many black leaders also expressed concern earlier in the year about Robb's alliance with white conservatives such as former representative Watkins Abbitt and former state appropriations chairman W. Roy Smith, both of whom supported school segregation during the Massive Resistance era here.

None of that seems to matter now when compared with black concern about electing a Reagan-style Republican. "Sometimes it's not so much a question of who you're for but who you're against," said Richmond City Council member Willie Dell, explaining her support for Robb.

L. Douglas Wilder of Richmond, Virginia's only black state senator, is widely credited with helping persuade Robb to moderate some of his positions in order to attract black votes. "There were a lot of meetings," said Wilder, who added he is not troubled by Robb's right-wing supporters such as Smith. "If he gets what he wants that's fine -- as long as I get what I want."

Wilder helped line up black leaders behind Robb by winning commitments from the candidate to support issues such as voter registration by mail and voting rights for the District of Columbia. The Coleman campaign has tried in recent days to turn those racially tinged issues against Robb in an effort to attract white conservatives.

Although they deny it, Coleman and his aides knew they were writing off the black vote when they positioned themselves on the hard right before the campaign even began. "The fact is, the black leadership is overwhelmingly Democratic," Coleman said in an interview. "In good times and bad they're going to vote for the Democrat unless there's some extraordinary circumstance."

In backing Robb, many of those interviewed said they knew nothing about his conservatism but were well acquainted with his family ties. "A lot of his votes are going to come because he's late President Lyndon Johnson's son-in-law," said social worker Carter.

Robb's biggest enemy in the black community may be apathy. "A lot of people seem real pessimistic," said Andrew Barker, a Richmond bank employe. "Both Robb and Coleman seem like they make a lot of promises but people are apathetic."