The fact that singer Stevie Wonder led yesterday's memorial to Dr. Martin Luther King, one of the largest black demonstrations in the country, says as much about the crisis of leadership in the waning civil rights movement as it does about the broad chord that Wonder strikes among black Americans.

The old warriors present at yesterday's march were eager to seize the moment and move the big crowd on the west steps of the Capitol beyond talk of a national holiday toward some more sharply focused direct action. The Rev. Ben Chavis of the Wilmington 10 urged moving out of a "winter of despair to a long hot summer." He got no response.

It was Wonder, with his lyrical talk and song about such old-fashioned matters as love, pride and excellence who got deafening cheers and seemed to better understand the yearnings of the legions of youthful marchers who braved the cold for the event yesterday.

He was upbeat and joyous without being Pollyannaish.

"It is not an easy time," he told the crowd, "and yet it is not a hopeless time."

Talking to reporters the other day, he had said, "I think that the people, young people, are really reaching out for something. It is important for those of us who have positions to respond, to acknowledge the fact that they are reaching out for that kind of oneness, that kind of tenderness."

These have been dispiriting times for blacks. President Reagan's budget cuts and the recession that followed them have fallen on blacks with heavy weight. Underlying, there are currents viewing blacks as sloths and welfare cheats. Racist jokes have attained a renewed respectability--Sixty Minutes' Mike Wallace, of all people, trotting out the stereotype about blacks and watermelon.

What seemed evident at the march and rally yesterday and what Wonder appeared intuitively to comprehend a bit better than the old-line civil rights groups like the NAACP, the Urban League and Operation Push, still reeling from the shock of the Reagan counterrevolution and unable thus far to find any rallying point, is that the assaults on the sense of pride of blacks have been felt as deeply, maybe even more deeply, at the assaults on their pocketbooks.

"You know we went over there and fought the wars in Vietnam, and we did just as much for this ---------- Commentary ---------- damn country as they whites did," said Gregory Vines, 22, a house painter from Washington.

There was to be sure ample talk from the podium and on the sidelines about the widely shared view among marchers that Reagan is no friend of blacks and is intent only on making the rich richer. But the day found its focus elsewhere--that King exemplified a black man who had made a large contribution to the nation.

The cheer that reverberated from the crowd on the steps of the Capitol throughout the bitterly cold day was, "We Want a Holiday! We Want a Holiday!" One of the large banners carried during the parade down Constitution Avenue to the Capitol, referring to the George Washington Birthday holiday, said: "If It's Good Enough for George, It's Good Enough for Martin."

"King did as much for whites as he did for blacks," said Peggy Cooley, who rode all night on a bus from St. Louis to be at the rally. "What he tried to do for whites is make them believe in mankind as a whole, that whites as well as blacks are human beings and that one day we will all be together."

Having a national King holiday, said Theresa Lucas, 27, a government secretary who lives in District Heights, "will mean a lot of white folks will actually be paid for a day off to celebrate a black man."

There were few whites at the march and rally yesterday but a varied assortment of young blacks--fraternity boys and their rich-faced girl friends in slinky fur coats ambling among porters, painters, secretaries and the unemployed--raising some doubts about the black conservative academics' theories of sharp class differences that have caused divergence in black aspirations.

Where does Stevie Wonder, the pied piper, the singer who tapped mood, plan to take his movement from here?

He said recently he will be back in Washington every Jan. 15 to lead a march until Congress enacts a national holiday for King. But beyond that he was careful to define his role as limited. He is not a politician, he said, but the "vehicle" for the expression of a mood and desire. He acted, he said, out of a feeling that if you just "wait on something you know has got to happen, it won't happen."