In the varicolored world of popular music, 1981 is likely to be remembered for the concert tours of two major singers, Mick Jagger and Joan Baez. The U.S. tour of Jagger and his Rolling Stones ended in Washington a few days ago. Baez's tour came earlier, in late spring when she traveled for five weeks to Argentina, Chile, Brazil and other Latin American countries. Both enjoyed success, though here the congruence of their talent ends.

Jagger stylizes himself as a coarse, joyless and self-absorbed pseudo-artist. He has the substance of cotton candy, spun into empty prettiness and tasteless fluff. When he sings in his song "Tops," "be a star in bed and never let success go to your head," or in the sexist "Under My Thumb," "there's a squirmy dog that once had her day," he brings to mind Paul Simon's remark: "The lyrics of pop songs are so banal that if you show a spark of intelligence they call you a poet."

They call Jagger a genius, which he is, though not at music. His acumen is that of P.T. Barnum and the showman's knowledge about the high birthrate of suckers. Instead of polishing his music, Jagger has merely polished his act. In the 1960s, he took to the stage in capes. Now he goes barebacked in white knickers. From capes to knickers: that's artistic development.

In appreciation for the tens of millions of dollars that people have been paying to hear him these past eight weeks, it might be thought that Jagger would at least keep up the pretense that the trippers were getting their money's worth. Not at all. He said to a reporter in Chicago that "popular rock 'n' roll songs are pretty trashy, aren't they? And ours included."

As the king of the trash pile, Jagger in his royalty likes to think that his reign is part of something larger than his own adenoidal yelping into a microphone. "The Rolling Stones is a traditional rock band," he says, "and that's its great strength."

Traditional?

How can a form of music with less than 25 years behind it have earned a tradition? It is straining even to say that a minor trend is at work.

In Latin America, Joan Baez was seeking to renew the energy of her folk singing with its only strength, the folk. In Argentina, she sang at a mass for the mothers of citizens who have disappeared. In Brazil, she met with labor leaders who have been punished for striking. In Chile, she sang in a free concert for a Santiago human rights group.

The primitivist governments in each of these countries found Baez and her music too threatening. She was denied permission to give commercial concerts. Banned in public, she sang in private-- in churches, homes and anyplace else where people gathered to ease their anguish about the systematic violence that is crushing them daily. Baez sang their own songs of hope to them, as well as those that have risen up from the repressed in other countries.

Amid the torturing and silencing that is standard equipment in these countries, Baez, even if she weren't a glowing artist of independent mind, would have still been a worrisome figure for the governments. She is the president of Humanitas International, a human rights organization. Founded by Baez two years ago, and based in Menlo Park, Calif., it already has 5,000 paying members. It is different from similar groups because Baez is an activist, not a theoretician. She will turn up in a Chile or a Northern Ireland, just as she went in 1979 to the refugee camps in Southeast Asia. She has denounced the "Stalinist leadership" in Vietnam as vehemently as the oligarchy in El Salvador.

Humanitas International, she says, is "quite simply, for the right to life. We recognize that Somali refugees, Salvadoran peasants and Cambodian children are not concerned with the fine points of Marxism or capitalism--they are struggling for their survival. And if what we can do in our small way aids in that struggle, then all our efforts are worthwhile." Those words have meaning. Aside from her persistent idealism and her commitment to nonviolence, Baez is matched by few performing artists for using talent on behalf of the world's poor.

Mick Jagger says that "rock 'n' roll songs tend to be about cars, food and girls." The music of Joan Baez is about peace, justice and freedom. The difference is large, just as the positive contributions to society by Jagger are as minute as those of Baez are immense.