There were a quarter million people at the Mall that day

It was not a political speech. It was more than a sermon. . . . It was a poem -- that address by Martin Luther King Jr. 20 years ago to a quarter-million people milling about between the Washington Monument and the Lincoln Memorial. He told them, ''I have a dream.'' They chanted it after him. He fused them into one.

The Civil War freed the slaves and started them toward independence. Now, said civil rights leaders, it was time for something more. Caravans of chartered buses rolled into Washington all night. Ordinary business ceased. The sale of liquor was banned. All street parking was forbidden. There were 6,000 policemen, firemen, and auxiliary guards on hand, with troops on alert nearby. Awed newspapers said ''100,000'' might come. (It was twice that.) Now all depended on the crowd itself. What was its mood?

I watched a double queue of demonstrators going down to the Mall past the Commerce Department building where somebody had put a sign, ''Please Keep Off the Grass.'' The visitors made an elaborate detour so as not to touch the lawn. They looked sweet-tempered yet terribly determined.

The weather was clear and mercifully mild. A huge green-and-white-striped tent was pitched on the grass on the Mall, lost in the gigantic throng. There was really not one crowd but two, divided by the long reflecting pool. The wall of faces seemed like a tapestry seen from the underside; you got to wondering what the design was on the far side: Had the weaver foretold the future, peaceful or warlike, pastoral or with trampling chariots?

At one point it seemed best for this reporter to climb under a truck, to look out at the throng in solitude, and make notes. There were a dozen themes on the placards. The program listed 10 speakers: Voices flickered on and off about different causes; the speeches were mostly dull, and the people on the speakers' stand milled about and distracted the audience.

Near the end came Martin Luther King Jr., the president of the Southern Christian Leadership Conference. As he was introduced, he received a big roar from the throng. People waited expectantly. He turned what had heretofore been merely a great spectacle into a crusade.

Without tricks of oratory, except for reiteration, speaking in a melodious and rather melancholy voice, he captured the vast audience, and put the gathering into a historic setting that linked it to the tradition of the past: with thinkers like Jefferson and old Sam Adams; with advocates of religious and personal freedom like Thoreau and Emerson and John Brown and William Lloyd Garrison; with political heroes like Lincoln and Wilson and Franklin Roosevelt. He interwove what they were doing under the arched sky with a liberal tradition of the past, from Gandhi, from the Constitution, from the Bible.

''Continue to work with the faith that honor in suffering is redemptive,'' Dr. King said. ''Go back to Mississippi, go back to Alabama, go back to South Carolina, go back to Georgia, . . . go back to the slums and ghettos of our Northern cities, knowing that somehow this situation can and will be changed. Let us not wallow in the valley of despair. . . .

''I still have a dream,'' he told them. ''It was a dream deeply rooted in the American dream. I have a dream. . . .''

Those listening caught it up as he continued. It was ''a dream that one day this nation will rise up and live out the true meaning of the creed, 'We hold these truths to be self-evident, that all men are created equal.'

''I have a dream. . . .''

They roared back this time. They had caught the refrain from the quiet, patient, firm tone.

''One day on the red hills of Georgia,'' he said, ''the sons of former slaves and the sons of former slave owners will be able to sit down together at the table of brotherhood.'' He paused.

''I have a dream,'' he repeated. Another roar in response.

''That one day even the state of Mississippi, a state sweltering with the people's injustice, sweltering with the heat of oppression, will be transformed into an oasis of freedom and justice.

''I have a dream.'' An answering roar.

''That my four little children will one day live in a nation where they will not be judged by the color of their skin, but by the content of their character.''

In their response he had them participating in what he was preaching.

Before that, the gathering 20 years ago had been a kind of holiday, an adventurous sort of Sunday School outing and political convention. Now he had made it into part of the American tradition, the revolt against kings and George III, the uprising against the 12-hour day in the American steel mills, the cry of Eugene V. Debs for economic equality. His invocation embraced all these causes.

I have a dream. Another roar!

''That one day every valley shall be exalted, every hill and mountain shall be made low, the rough places will be made plain, and the crooked places will be made straight, and the glory of the Lord shall be revealed, and all flesh shall see it together.''

It was moving; almost overpowering on that tremendous multitude.

What did that gathering 20 years ago accomplish? The Soviet daily Izvestia placed the rally on the front page (misinterpreting it as always). It brought major headlines in the British press. It helped pass the great civil rights laws of the Kennedy and Johnson administrations.

It was noticeable that some 40 percent of the demonstrators were white.

I walked away that evening watching block-long lines of people waiting patiently to buy ''Good Humors,'' and admiring the way street hydrants had been hitched up to make drinking bubblers. Next day the New York Times carried a front-page story by James Reston headed, ''I Have a Dream,'' but most papers, like the Washington Post, gave it only a mention. It recalled 120 years ago, after the ceremony at the Gettysburg battlefield cemetery, when few papers carried the text of the President's speech. After all it was only 300 words long. ''President Lincoln also spoke,'' many papers said.

Efforts today to revive the exultation of the 1963 march are uncertain. Crowds fill Washington, but there is question of a consensus in America with its conflicting problems.

Yet nobody who watched here 20 years ago can doubt that if the need arises, somewhere in America a voice will rise, crying, ''I have a dream.''