For two decades, he was a musical child prodigy dishing out some of the liveliest of the Motown sounds--"Fingertips," "Uptight," "My Cherie Amour," and other songs with "do-wop" lyrics: I was made to love her, Worship and adore her. Yeah, yeah, yeah.

Now "Little Stevie Wonder" has grown up, six feet tall in life and larger in legend. He is 31, and his music has become increasingly political--songs about Vietnam veterans without jobs, blacks who, he says, have cash but can't cash in their faces when it comes to finding a house and about his crusade to have Martin Luther King's birthday declared a national holiday: You know it doesn't make much sense. There oughta be a law against Anyone who takes offense At a day, in your celebration . . .

Wonder, in town to complete plans for Friday's march in honor of King's birthday, has over the past few years become an odd man out, one of the last crusaders at a time when most popular music is about funk, freaks and infidels.

In life and in his music, he is different because he cares to be.

"It's not my job," he said of his efforts to nationalize King's birthday during a luncheon interview yesterday with editors and reporters from The Washington Post. "It's my pleasure."

Wonder, wearing his usual dark glasses but having changed his hair style from braided and beaded corn rows to an Afro, at first appeared ill at ease and asked if anyone had seen the movie "Elephant Man," about the struggles of a physically handicapped man.

He quickly relaxed, however, and when asked when he first knew he was blind, Wonder joked, "I haven't realized it yet . . . Between me and you, I'm going to get into your car when I leave and drive away."

Wonder did not need his role as a champion of King's birthday to make him unique among musicians. He already had established himself as not only a prolific song writer and winner of numerous music awards, but also as someone whose music frequently carried a social message: You just could not know how long we tried, To see how this building looks inside. This must be a lucky day for me, Because the sign says there's a vacancy. Look, I know you came a long way, But you made it just too late. So we had to give it to somebody else.

Wonder said yesterday that this song, "Cash In Your Face," reflected his own experience in trying to find an apartment in New York once when his wife was pregnant. When he mentioned to the prospective landlord that he played piano, the landlord, who had previously voiced no objections, suddenly became skittish.

"What happened in that case was just that they were afraid of what they didn't know," Wonder said. "They assumed that it was going to get loud."

Many of his songs have been about similar trials and tribulations of survival in America, he said. "I wanted to do a song about what was happening in Atlanta called 'Peachtree Plaza Doesn't Smile Anymore,' but I just didn't finish it in time," he said.

Wonder, who has become something of a folk hero among many blacks, especially black youth, asserted yesterday that many youngsters are going through a serious identity crisis.

"I see people relating more to trying to be like what they see on films and television," Wonder said. "Even families basically can communicate far better, unfortunately, if they are watching some soap opera.

"They are so much into the outer, you know, the outside world--what's happening on this and what's going on there--that they really do not take the time to spend with each other, to get into each other, to get into families."

Many, including civil rights leaders like the Rev. Jesse L. Jackson, have criticized much of the music now played on radio stations to contributing to the problems of younger blacks. Too many of those songs, critics say, focus on sex, drugs, good times and fantasy.

Wonder, saying that he did not believe every song has to have a social message, refused to criticize other entertainers and recording artists, saying parents could be effective in curtailing any possible adverse influences from the music.

"You cannot stop a person's creativity, you cannot say, 'Don't do this, don't do that,' because then it's not freedom of the creator or of the writer," he said.

"If you educate that child, you tell them what is wrong, tell 'em what that's all about," he added, "then certain things just will not happen."

Last Jan. 15, Wonder led a crowd estimated at 35,000 by U.S. Park Police on a march through Washington that began at the Capitol and ended with a rally on the Washington Monument grounds. Since then, little has come of the efforts to make King's birthday a national holiday. Wonder said yesterday that he will lead other marches if necessary.

"I'll do it for as long as I have to," he said. "I really think that with what is happening in the world, with more and more people talking about being born again Christians, I think that people--young people--are really reaching out for something."

"It is important for those of you that have positions, or those of us that have positions, to respond," he said, "and to acknowledge the fact that they are reaching out for that kind of oneness, that kind of tenderness."