The nay-sayers have recently come out in force against the idea of a black presidential candidacy.

Just a week ago, on the television program "Good Morning America," author and political analyst Theodore White said that a black presidential candidate would probably destroy the Democratic Party, at least for a decade. "The black vote is part of the inherited property of the Democratic Party," White said. "They vote 90 percent Democratic."

Strategists for some of the leading white candidates regard Jesse Jackson as a threat in the Democratic primaries because he would siphon off the black vote. Others say a black candidacy would hurt the black cause.

But the grenade-lobbers are too late; what has occurred since the idea took fire several months ago has already proved the viability of the concept.

Two years ago, the media were saying that the political influence of blacks had fallen to its lowest level in two decades.

Today, building on the momentum of Harold Washington's victory, Wilson Goode's probable win in Philadelphia and the idea of a black presidential candidate, black influence is spiraling and black concerns have been thrust upon the agenda of the Democratic Party.

Former Vice President Walter Mondale, who campaigned for Harold Washington's opponent in the Chicago Democratic mayoral primary and later supported Washington against a Republican in the general election, now speaks out against Ronald Reagan's firing of three members of the Civil Rights Commission and is pushing the Democrats to increase their budget for voter registration from less than $150,000 to $4 million.

Sen. John Glenn has come out in favor of affirmative action and says he has voted against amendments designed to prohibit approaches such as numerical goals and guidelines. Sen. Ernest Hollings of South Carolina has endorsed the idea of a black or woman as a vice-presidential candidate. Black leaders who were being ignored suddenly are receiving position papers on where the candidates stand on black issues.

Jesse Jackson's strategy--to make sure that blacks were no longer taken for granted and considered "the inherited property" of the Democratic Party--clearly is working.

Jackson has also created much excitement and interest in voter registration among blacks, igniting dynamics that can put them in a good position for the primaries for the first time in political history. "We're talking about registering people to vote six and seven months before the first primary," said Joe Madison, the director of political action for the NAACP, "and that increases our participation in selecting candidates."

The strategy that emerged from a meeting of a small group of civil rights and political leaders in Chicago last week was to endorse the concept of a black candidacy in order to free Jackson to run in '84, while pushing a "people's platform" as a guide to all of the candidates.

It's true that a black candidate could hurt Mondale. But there are responses that Mondale could make. He could slate more blacks, which would divide the black vote. With both candidates going after black votes, you whip up more interest in the black community, increase the number of black delegates to the convention and enhance voter registration.

But some strategists seem to have stopped thinking and are engaging in the kind of nay-saying that often emerges when a new phenomenon comes upon the scene. Blacks were told their cause would be hurt when Thurgood Marshall and other NAACP lawyers decided to shun gradualism and push for full school integration. Martin Luther King's civil rights movement, the student sit-ins, the March on Washington were, in the opinion of some, potentially hurtful to the black cause. So beneath the cool analytical exteriors of some are mental barriers to the very idea.

Jackson's stump through the South already has shown he can deal with issues the other candidates aren't talking about and win the ear of the white poor as well as blacks. And with Jackson third in the polls behind Mondale and Glenn, he seems to have more credibility than many of the other candidates.

But most of all, blacks have gained a firm place on the Democratic agenda, and that is positive proof that, for the present at least, the idea works.