Daddy King; Why he keeps on keeping on; Daddy King: An Autobiography, by the Rev. Martin Luther King Sr., with Clayton Riley. New York: William Morrow & Co. $10.95

The jacket photo shows the Rev. Martin Luther King Sr. at a moment when millions of Americans remember him -- rousingly delivering the benediction at the final session of the 1976 Democratic convention. This year he was on the same podium, and later his Ebenezer Baptist Church in Atlanta was in the news as the place where President Carter made the attack on hatred and racism that he had to deny was aimed at political opponent Ronald Reagan.

But few have known what this simple, engaging, and (there is no more fashionable word for it) inspiring autobiography informs us: that "Daddy" King told Jimmy Carter he would support him in 1976 only if "a certain Republican" -- namely, "my old friend" Nelson Rockefeller -- did not enter the race.

There had been a classic conversation when Mr. Carter interrupted a King nap to see if the minister would support him if he decided to run:

"'Run for what?' I asked him.

"'Why, for the presidency,' he answered.

"'The presidency?' I said. 'Of what?'

"'The United States,' he told me.

"I had to admit to some surprise."

But Rev. Mr. King's own achievement, starting far behind the goal line of American society, is no less surprising than a Jimmy Carter drive to the presidency. Talk about "we shall overcome!" Young Mike King didn't know how ignorant he had been left by the country "school for Negro kids" until he went to the city as a preacher. He swallowed his pride and began over again in the fifth grade. He rose in the ministry to shepherd the largest black congregation in Atlanta and, in the community, to become a fighter for the vote and other civil rights many years before son Martin Luther King Jr. emerged as a national leader.

The assassination of this son, the drowning of another, the murder of his wife while she sat at the organ in their church -- all the personal tragedy accompanying the happiness of warm family bonds -- is kept in the perspective of a man whose faith in God cannot be shaken. The prose sounds like the man, not maudlin, not overwrought, but conveying the heartbreak and the lasting hope. There is humor, too, as in the folklike turns of phrase from Mike's youth.

Along with the King family story there is the civil- rights story, the involvement of Martin Jr., the tensions among those who didn't want to rock the boat, those who wanted to rock it violently, and those who wanted nonviolent action. Exposed to violence in his boyhood, witnessing his mother do battle on his behalf, the senior King nevertheless learned nonviolence, learned from his mother to love instead of hate. What has made him keep on keeping on? Maybe a few sayings of Daddy King will help to explain:

"It never did enter my mind that I wouldn't become successful."

"In the act of faith, every minister became an advocate for justice. In the South, this meant an active involvement in changing the social order all around us."

"Our struggle was not so much against other people as it was against the systems people had created to keep us from living decent lives."

"For a white person to support our struggle required more strength than most folks had. But for the Negro, the struggle had no escape hatches; only whites could quit."

"Counting on the basic human decency of all peoples was the best way to get anything accomplished if it involved fundamental changes in the way folks had lived most of their lives."

"I never believed in political action that did not come out of a set of ethics, a sense of fair play, a high regard for the humanity and the rights of all people."

"People can accomplish all things God wills in this world; hate cannot."

"You and I know these are bewildering times we live in. But don't lose your way and don't ever let it get so dark you cannot promote a song."