LEXINGTON, Ky. - She is the high priestess of pop music, the golden-haired muse of the young and innocent. Her voice, like her music, is a sea gull flying free and high. Sometimes it soars, sometimes it swoops, sometimes it even gets so close you almost can reach out and touch it.

Almost, but not quite, because Joni Mitchell's music has a quicksilver quality about it that is hard to pin down categorize, label or define. It's a little rock, a little folk, a little jazz, a lot pure Joni and her symbolism, romanticism and mysticism.

She came to the University of Kentucky Monday night and put on a concert to remember. Backed up by the talented LA Express, but often working alone, Joni sang her songs, played her guitar and piano and took her adoring audience on a trip of "Rows and flows of angel hair/ And ice cream castles in the air/ And feather canyons ev'rywhere."

In a time when pop music often seems to be spinning its wheels, when volume sometimes is mistaken for genius, Joni Mitchell still is an artist who takes it to the limit. Worshipping at the feet of her very personal and very real muse, whom she whimsically calls "Art," Joni writes all her own music, sings it, accompanies it expertly on guitar and piano and even packages it by painting her own album covers.

Her fellow entertainers stand in awe of her talent. Linda Ronstadt told Time magazine that "Joni is the first woman to match any man on his own terms as a songwriter, guitar player or as an incredibly magnetic human being." And Stephen Stills says that "she reaches way down and grabs the essence of something very private and personal to women."

Her musical poems satisfy on a surface level, due to her clear soprano and haunting melodies, but also on a deeper, more intellectual level. Nevertheless, her work also is an overwhelming commercial success - proof that an artist doesn't always have to compromise to put bread on the table.

Her albums sell in the millions and her concerts always are sold out in advance. When the University of Kentucky announced that Joni was coming, students brought sleeping bags and camped overnight so they might be first in line to get choice $6 tickets close to the stage. All 8,000 were sold within hours.

All this has made Joni Mitchell a millionaire several times over, a star able to command $18,500 for a single show, as she did at UK. Yet, sometimes, as in "For Free," she is somewhat fretful and self-mocking about her material success:

"Now me I play for fortune
And those velvet curtain calls
I've got a black limousine
And two gentlemen
Escorting me to the halls,
And I play if you have the money
Of [sic] if you're a friend to me
But the one-man band
By the quick-lunch stand
He was playing real good, for free"

Ever since Rolling Stone magazine did a story that purported to delineate Joni's various love lives, she has become what she describes as a "media dropout." She doesn't watch TV, read the papers much or grant interviews. The members of the LA Express and the rest of her entourage are protective of her privacy.

"What's the need for interviews?" asked her road manager during Joni's show at Memorial Coliseum. "She's not out to hype anything. She just wants to play her music. Now I don't want you writing down anything more I say. Just go out and listen to the show, okay?"

She and her troupe flew into Lexington Monday afternoon from Raleigh, N.C., and were taken in chauffeured limousines to the Hilton Inn. At the hotel, Joni requested that a piano be brought to her room, ostensibly so she and her muse, the mythical "Art," could work out some music together.

When Joni arrived at the Coliseum at 7:35 p.m., she found the floral bouquets and poems that her fans always bestow on her wherever she goes. Later, on stage, the various shows of affection ranged from raucous shouts of "JONI, I LOVE YOU!" to the traditional lighting of matches when she left. On stage was a vase of red roses sent by an admirer.

Although she is beautiful, in her way, her attraction doesn't depend on physical attributes. Unlike Linda Ronstadt, who is apt to perform in a loose-fitting blouse and tight cutoffs, Joni plays down her feminity [sic] - and, in the process, plays up the mystery that surrounds her. At UK, she came on stage wearing a pin-striped gray suit, dangling earrings and with her vibrant blond hair tucked under a floppy felt hat.

She puts on a dignified, high-class show. Although she had been bothered by an upset stomach, she came on stage at 9:30 p.m. and played for two hours, with only a 10-minute break. She and her pure, clear soprano caressed her poems so wonderfully that the mood of the audience mirrored the mood of Joni's work - thoughtful, tender, slightly melancholy. At a Joni Mitchell concert, people pay as much attention to the message as to the music.

Once the grind of the road showed on Joni. She started a song, did a few bars, messed it up royally and finally quit, laughing. However, the audience didn't seem to notice and began to applaud, as if she had done it perfectly. That caused Joni and the LA Express to laugh harder, shaking their heads at the wonder of it all.

Then the muse was gone, leaving her followers satisfied but somewhat sad. Time had passed too quickly. Or, as Joni sings, "Don't it always seem to go/ That you don't know what you've got/ Til it's gone."