THERE IS A BIT of "thou dost protest too much" in the blanket denunciation by many blacks of the Rev. Ralph David Abernathy's endorsement of presidential candidate Ronald Reagan. Must a man be drummed out of the human race because he takes a position that is out of step with the thinking of the majority? Ralph Abernathy is not, after all, a Pied Piper behind whom millions of blacks are likely to troop in answer to his call.

But even if he were, doesn't he deserve the freedom of choice? That, after all, is progress, the freeing up that each black desires -- the right to choose -- even if he chooses the devil.

On close examination of his reasons, Abernathy actually makes a point that many other blacks have made. "The Democratic Party in Washington," he said, "is not going to understand that black people are part of America until we let them know we do have an alternative."

In other words, if President Carter has not kept his campaign promises to blacks but the black vote continues to be dutifully and predictable Democratic, then blacks have lost a valuable bargaining chip.

Beyond that, I think the effect of one party presuming it has a bloc of 10 to 17 million voters in its pocket is to lower the worth of the candidates in both major parties. If the Republicans assume that blacks will always go Democratic, what then is the point of putting up a candidate they might find appealing? If the Democrats assume that no matter who their candidate is, blacks will vote Democratic, what is to spur them to run their highest-quality candidate? So long as blacks are in the pocket of one or the other party, it keeps each bidding lower rather than higher for the black vote, and thereby cheapens the quality of the candidates the whole country has to choose from.

While this election does present voters -- both black and white -- with difficulty in choosing, I can't agree with those whose solution is to boycott the election as a protest. It is necessary to choose even when there apparently is so little to choose between. Who ever said democracy promised easy choices? Who ever said democracy promised success? It promises only the right to choose. And it is when we fail to exercise that right that we fail to exercise all that is guaranteed.

That is the exercise many of us went through in 1968. We stayed home because there was disappointment with Hubert Humphrey's failure to stand up publicly against the war in Vietnam. Look at what we got.

It was Edmund Burke who said that the only thing necessary for evil to triumph is for good people to do nothing.

In that regard, we could all learn a lesson from the dramatic success story of black women and the ballot over the last 20 years. Quietly and unobtrusively, they have increased their voter turnout at a faster rate than have black men and during a period when the turnout of whites, both male and female, has declined.

Sandra Baster and Marjorie Lansing, authors of a new book, "Women and Politics," estimate that only one-quarter of eligible black women voted in 1952 and 1956, but the number jumped to 76 percent by 1976.

The increase is all the more remarkable because it contradicts the classic political theory that the more disadvantages of the prospective voter, the more alienated is that voter and the less likely he (or she) is to go to the polls. A dramatic increase in voting has been the black woman's answer to her disadvantaged plight.

While Baxter and Lansing are "puzzled" by the explanation for the voting pattern, women's leader Dorothy Height has ideas of her own.

"It's the organized life of women -- the groups that we belong to put voting on their agenda," she says. "Black women never have felt free just to have social activities. The plight of our family and our children has driven us to action." The powerful independent black church and black women's forced economic independence as household heads also are strong factors.

Part of this progress brings us once again to Ralph Abernathy's endorsement of Reagan. Just as we give Coretta King and Jesse Jackson the right to choose Carter, we must free up Abernathy to choose his candidate -- even if, as is likely, very few follow his lead. It marks a coming of age of the followership, the-rank-and-file, when from a plethora of leaders, there is less than unanimity.

And this doesn't rule out the possibility of blacks as a powerful bloc. It is only when that bloc is automatically assumed and guaranteed that the vote is cheapened.

But the real question that has to be considered in the end is whether sending a message to Jimmy Carter is worth getting Ronald Reagan elected as the next president?