San Francisco - This was one of those beautiful moments in which success goes far beyond planning or experience.

Joni Mitchell and the five-man a capella group, the Persuasions, sang a gospel-tinged "Shadows and Light," and brought the audience of 7,000 to its feet, all cheering, many with tears of joy streaking down their faces.

Singer-songwriter Joni Mitchell recently embarked on her first tour in several years. Judging from her City Auditorium shows Friday and Saturday, before a total of 14,000 fans, it was a deeply moving success.

Music as an art form - which is how Mitchell regards it - should do something besides take people's money and leave them with some hummable tunes. It has grown out of a need to communicate feelings that go beyond just words. When the conditions are just right, the musicians and audience become on, basking in the shared emotion.

And that is what happened at the Civic.

Her appearance at last May's Berkeley Jazz Festival was far from satisfactory. She had assembled an all-star jazz band to help perform her collaborations with the late Charles Mingus, but the overabundance of talent on stage never went anywhere with the music.

In the early '70s her touring band, L.A. Express, provided pop-jazz backing, but she soon left it far behind as her works became less repetitious, more linear and dependent on the growing awareness of jazz improvisation.

Mitchell's musical growth has been chronicled in her recordings. The recent "Mingus" and 1977's "Don Juan's Reckless Daughter" have been made with the aid of Herbie Hancock and the musicians in Weather Report.

Because Mitchell abides by her own rules of music only, her experiments have confused and sometimes alienated old fans and jazz buffs alike. What's this untrained singer doing playing with a form in which she has no? Why doesn't she go back to singing her old songs, "Both Sides Now" and "Woodstock"?

This new tour proves that Mitchell does know what she's doing.

She has hired some of the youngest and most well-known names in jazz-fusion for her all-electric quintet (even Mitchell plays electric guitar), then given them plenty of room to play: Weather Report bassist Jaco Pastorius, saxophonist Michael Brecker, guitarist Pat Metheny and his pianist Lyle Mays are all in their twenties. Mitchell is 35 and her percussionist, Don Alias, is older.

The bulk of the show's songs came from her mid-'70s albums. "Hissing of Summer Lawns" and "Hejira."

Over the course of two hours and 20 songs Mitchell gave each player a chance to make his statement. But it is the mixing and juggling of musicians during various numbers that was most rewarding.

While Joni sang the lyrics to "Dreamland," Alias played congas and the others added various percussion sounds. When Mitchell finished "The Dry Cleaner from Des Moines," Brecker took a long bop-based sax solo. Pastorius repeated his standard bass theatrics; Metheny and Mays added some crystalline beauty to "Amelia."

Songs featuring the entire band were vibrant, but often cluttered and mechanical, obscuring the lyrics. Yet, as the show progressed, the bond between audience and performers grew until the climactic "Shadows and Light."

The gospel-based Persuasions opened the show with do-wop versions of R&B, soul, pop and gospel songs, all done with just five voices and no instruments.