WASHINGTON'S black community raised its collective eyebrows last week when the three presidential candidates invited to a convention where national black leaders were writing a public policy agenda for the 1980s suddenly decided not to show up, forcing that particular forum to be canceled.

This has led to puzzlement and, in some cases, humiliation on the part of blacks. "It's a gross insult," said one professional man in his 30s. "I can't believe that we could hold a meeting and they could thumb their noses at it," a woman in public life added. "It hurts."

Watching from the sidelines, however, one is struck by what seems to be on some people's part, at least, a wrong reaction to the whole affair. They are acting as if it was somehow their fault only that the candidates didn't show up.

But when it comes right down to it, the three candidates -- Sen. Edward M. Kennedy, Rep. John Anderson and Gov. Jerry Brown -- simply chose to concentrate on their New England primary battles instead.

It's also safe to say that none of the candidates would have been willing to say what blacks at the conference wanted to hear. With the country in a militaristic, budget-slashing mood, it should be no surprise that these candidates would not welcome having to answer to an audience rightly speaking out for a part of America that wants to expand businesses and job opportunities and increase aid to Africa and the Caribbean.

A disturbingly strong case also can be made that the candidates snubbed the gathering because, after having decided it was not in their best interests to appear, they thought they could cancel without suffering any harm at the polls.

The basis for such reasoning on their part would be a belief that blacks don't vote and can be taken lightly. Those blacks who do, the reasoning would go, can be taken for granted by the Democrats and ignored by the Republicans.

I have been talking to black leaders who urge as a response to the candidates' cancellation a massive turnout of black voters. "Don't get mad, get smart," they are, in effect, saying.

The blacks who were at Richmond represented about 300 organizations that touch nearly every area in the black community. They left Richmond, the leaders say with extra resolve to register voters -- particularly the young.

"People will now be more eager to ask those hard questions which we are posing for voter mobilization in the Congress and presidential campaign," M. Carl Holman, head of the National Urban Coalition, told me.

I would like to see black leaders and black organizations -- sororities, churhces, social groups, fraternities -- mobilize in a voter registration drive that would have a significant impact on the 1980 election.

In the collective black leadership was kicked in the teeth because they were perceived to be too powerless to deliver votes as many Washingtonians told me they believe, then a fighting spirit would be aroused in the rank and file.

But I would like to see that challenge further answered by selecting a primary and a candidate and delivering to that candidate a victory as a further demonstration of power. I'd also like to see that power solidified in Illinois behind John Anderson. Former senator Edward Brooke suggested that strategy in Massachusetts and blacks gave Anderson 60 percent of their vote, Carter 48 percent and Kennedy 51 percent.

Eddie Williams, president of the Joint Center for Political Studies, doesn't think there is time for my idea to be put into effect before the Illinois primary.

He thinks that if the blacks who are registered turn out to vote, and if there is concentration on registering the young, there is time to make an impact on the presidential election and other elections.

Not many people believe that you can build mass participation without setting forth specific goals, but people who have stayed away from the polls because they didn't think their votes would matter should by all means now rethink that negative mind-set. It has become a self-fulfilling prophecy. n

For if there is any underlying message in the candidates' decision not to appear, it is that blacks must become more self-reliant, must build up their own institutions, powers, and yes, numbers. It is a sure bet if the leadership had those numbers before Richmond, the candidates would have come.

In 1976, black voters were a major influence in the election of President Carter, but they have been deeply disappointed with the Carter administration. The rules of politics seem to have changed. The old quid pro quo dictum now seems a qualified one. The "You Owe Me" philosophy -- under which blacks had felt that, because they had supported certain candidates in the past they deserved to be heard -- is being disproved.

The collective leadership at Richmond sought to play down partisan politics. They stressed instead unity and self sufficiency.

But it seems the first test should come before the parties have selected their candidates. Perhaps Eddie Williams is right about Illinois. But certainly there must be other primaries where a similar strategy could work. And the Richmond conference warnings about partisan politicking notwithstanding, they would be unity and self-sufficiency.