LENOX, Mass. - Joni Mitchell's concert at Tanglewood Tuesday should have provided lyrical. harmonic and melodic stimulation, deriving an appreciation on a totally intellectual level.

It did this, no mistake about it. But the singer-songwriter and her band of electronic jazz stalwarts also supplied a totally exciting, satisfying, entertaining, evening. Her show was a legitimate cross of rock, jazz and ballad pop, easily among 1979's best live acts to grace this area..

Her first tour in three years continues her flirtation with jazz styles with heavy doses of her tribute collaboration project with and for the late jazz bassist, band leader and composer, Charles Mingus.

She has assembled a fitting electric jazz counterpart to last year's Milestone Jazzstars tour, the crest of fusion music. Guitarist Pat Metheny, keyboardist Lyle Mays and bassist Jaco Pastorius have extended their instruments tonally by leaps and bounds the last two years, while saxophonist Michael Brecker has participated in various artistically satisfying jazz-rock projects in the Becker Brothers Band and in Dreams.

The show started with familiar numbers led by an exciting Big Yellow Taxi expanded by Mays' keyboards. The first big applause getter was her 1974 hit Free Man in Paris, which had an almost big band sound from Mays and Metheny's chords and Brecker's horn riff.

Brecker drew some of the warmest applause, deservedly, with a blue solo on the Mitchell-Mingus opus, Pork Pie Hat, a tale of American racism through the story of Jazz great Lester Young.

Each musician was well-featured in a solo format. Pastorios lit into a full five minutes of bass runs, with his individual brand of cording harmonics, that quoted, among other things Duke Ellington's Sophisticated Lady and the theme from Lawrence of Arabia.

Metheny followed with an extended set of musical ideas leading out of Ms. Mitchell's ballad of romance and airplanes, Amelia, and led the band into another jazz-styled piece featuring Latin rhythms.

But, of course, Ms. Mitchell's engaging personality and surprisingly strong singing voice commanded the show. Her songs ranged in texture from the sad and sullen Amelia to an ethereal rendition of Woodstock to a confessional The Last Time I Saw Richard to the wit of God Must Be a Boogie Man.

She sang all of these songs as ballads, giving each a sense of individuality that went beyond words and instruments.

A lot of them with marvelous instruments could just as well be singing off a tomato soup can, unlike Billie Holiday, who no matter how banal the lyrics always sounded profound.

Mitchell said she got a very broad education in a very short space of time about jazz, but that she also learned a lot about the various factions among jazz musicians and listeners. She said she very much so made some discoveries as a singer.

It was a great exercise, it really stretched my range and freed up my phrasing incredibly. I have more freedom, more options on how to phrase. I don't think I'd ever sung a song with quite so much movement (as Pork Pie Hat'), yet it's one of the most comfortable songs in my show now. I just love to sing it.

Will there be a change in the direction of the 35-year-old singer's career as a result of the Mingus experience?

I don't think so, she said. It seems, judging from acceptance on this tour, that people grasp the eclectic nature of my show and appreciate it. They seem to be willing to embrace all these little sojourns into various fields equally, which is really quite surprising. I'm gratified.

Although backed by essentially jazz musicians (the forementioned Pastorius on bass, guitarist Pat Metheny, his pianist Lyle Mays, saxophonist Michael Brecker, and drummer-percussionist Don Alias, formerly with Miles Davis and Blood, Sweat and Tears), Mitchell's two hour show will include, as she indicated, all kinds of music, just as her career has.

She once said, Pigeonholes all seem funny to me. I feel like one of those lifers-educational types that just keeps going for letter after their name. I want the full hyphenate: folk-rock- country-jazz classics. So finally, when you get all the hyphens in, maybe they'll drop them all and get down to just some American music.