The prospect of a black presidential candidacy and a progressive agenda in 1984 grows stronger with each passing day. Mainstream commentators and politicians have sought to trivialize the interest behind such a candidacy, but the more they try, the stronger it grows.

Staring them in the face is the unexplainable occurrence of an unannounced and unfunded black leader, the Rev. Jesse Jackson, who in a recent national preference poll scored third among Democratic candidates, well ahead of a few contenders who have built massive organizations across the country.

The momentum that is building behind the idea is no freak occurrence or accident. There are good reasons for this remarkable achievement that have a history behind them--a growing voter registration drive among minority citizens, black and Hispanic; the emergence of an alternative political platform within the Democratic Party; and a growing alienation with mainstream politics, whether practiced by Democrats or Republicans, that of late has become politicized and credible.

Jackson, who has personally undertaken a major black voter registration drive in the southern states, has called on 16 million eligible black voters to register this year and become the cornerstone of a "Coalition of the Rejected" to transform the politics of this nation. In the 1980 election, more than 75 million eligible voters failed to vote for a presidential candidate. With only 8.3 million out of 16.4 million eligible blacks voting, the potential is enormous.

The depth of alienation with mainstream politics also has to be reckoned with. Harold Washington's mayoral victory in Chicago earlier this year is an illustration.

Washington won by arousing the electorate around issues and programs. He tapped the alienation, in this instance of black Democrats in Chicago--as well as a significant number of white Democrats--who had been taken for granted for years without gaining access to party support on the issues that mattered. The Washington lesson is that an office-seeker who has something to say about historical class concerns against inequity and injustice will catch on with the voters, regardless of race, even without having a multimillion- dollar war chest.

Translating excitement into turnout at the polls requires both voter mobilization, which now is in place, and a political program--a rallying point-- that meets the felt needs of untold numbers of citizens who up to now have been left out of the political process. No one who has been part of the coalition for an alternative is so naive as to believe that the only approriate candidate has to be black.

For this movement to be successful, it will ultimately have to stir the imagination of working men and women as well as the have-nots. If black voters turn out to be the cornerstone of the effort, that is simply a reflection of the source of the momentum at this particular stage in the process, not the final outcome.

For the past three years, the Congressional Black Caucus has developed an alternative budget and set of federal priorities that have gained increasing acceptance across a broad spectrum of labor, civil rights, women's, environmental and peace organizations. The alternative has spelled out a national program of full employment, military conversion, tax reform, a nuclear freeze, and international cooperation that has challenged the alienative mainstream policies that have characterized both Democratic and Republican administrations in recent years.

The rejection of the caucus alternative budget in Congress has not spelled an end to it. On the contrary, across the nation, citizen coalitions and local governments have embraced the caucus program in a number of cities. It also has led to the development recently of a "people's platform" that has won the support of the broad-based civil rights coalition sponsoring the 20th Anniversary Mobilization March in Washington Aug. 27.

Ultimately, ideas rather than personalities are the shaping force behind political change. There is a growing sense today that the Tweedle Dee and Tweedle Dum politics practiced by both Democrats and Republicans has ceased to furnish the answers to the real problems of jobs, justice and peace that afflict so many citizens.

A progressive, black presidential candidacy has unsettled mainstream leaders not because of the color or personality but precisely because it is wedded to an alternative political program that speaks to the alienation of so many and makes far more sense than the mainstream policies that it seeks to replace.

It just so happens that the individual who has most convincingly articulated this alternative is a black leader. The combination of such a leader and an alternative vision of the future might just move America toward building the kind of society that it has so long aspired to build.