President Reagan is said to be surprised and annoyed that American blacks do not identify him as a firm friend of civil rights--a perception that, given his good instincts, may be a bit unfair.

Yet it took the president most of a year to come to a clearly defined position on the pending issue that matters most: the renewal, and strengthening, of the 1965 Voting Rights Act. And this position was less voluntary than inescapable. A bipartisan coalition had already done the work, passage was assured, and a veto unthinkable.

Follower-ship in the White House, it is fair to recall, is no new thing. Dwight Eisenhower, though he finally sent troops to Little Rock in 1957 to enforce compliance with court orders, never moved beyond a "petulant neutrality" on the merits of the Brown decision. John Kennedy, while more explicitly supportive, usually found himself trying to contain, not lead, racial events.

Only Lyndon B. Johnson (who told his attorney general, Nicholas Katzenbach, to "write the god- damnedest toughest voting rights act you can devise") managed to anticipate and shape the rapid shift of national sentiment on civil rights.

The foregoing are among many lessons made clear in Harry Ashmore's splendid new book, "Hearts and Minds," subtitled "The Anatomy of Racism From Roosevelt to Reagan." Ashmore is a South Carolina- born editor who knows the ins and outs of the civil rights "revolution" as well as any American white. Reagan, and most of us, could learn from him. 4 As recently as 1910, Ashmore observes, the tenth edition of the Encyclopedia Britannica concluded that ". . . the negro would appear to stand on a lower evolutionary plane than the white man . . . more closely related to the highest anthropoids." "No savant anywhere in the western world," writes Ashmore, "arose to challenge" such complacent pseudo- scientific insult.

Despite such obstacles, Ashmore's book reinforces a heartening impression: how high racial barriers have usually looked in prospect, yet how untenably arbitrary and fragile they proved to be under active challenge.

All along, the latent moral power of the civil rights cause was underestimated--as was the modesty of every opening challenge to Jim Crow. When, for instance, Martin Luther King Jr. emerged as the leader of the Montgomery bus boycott in 1955, it was not to seek the full integration of buses, "only that blacks be seated from the back of the bus on a first-come, first-served basis, and that whites . . . not be given an absolute priority on seats when there was an overlap."

Ashmore emphasizes throughout his book how conservative and traditional black aspirations were. In 1963, when "black power" had joined organized white resistance among the petty diversions of the day, he was writing: "The mass of American negroes do not reject the existing social order, seeking only to share fully in its bourgeois blessings."

Precisely how those "bourgeois blessings" might be secured has all along been problematical. But "Hearts and Minds" is not, again, a depressing story. From the blinkered racism of 1910, and the illusion of "separate but equal," to the present is, after all, an impressive success story. But it is also a story of unfinished work.