Joni Mitchell will never be mistaken for a femme fatale rocker like Pat Benatar or Joan Jett. The Lady of the Canyon is just too, well, sensitive for that.

This is a woman who sings about love- love sought, love found, love abandoned- with irony, wit, and a keen eye.

So when Mitchell tore into a party rocker like (You're So Square) Baby, I Don't Care from her Wild Things Run Fast album last night before an audience of about 7,000 at the Finger Lakes Performing Arts Center in Canandaigua, it came as something of surprise.

A pleasant surprise at that; this lady can rock. Even familiar songs like Free Man in Paris or Help Me had forceful, rocking arrangements, with Mitchell playing electric guitar and stepping back to trade riffs with her sidemen.

THE CONCERT shows Mitchell's shift away from the experimentation with that increasingly dominated her albums of the late '70s, from The Hissing of Summer Lawns and Hejira in 1976 through Don Juan's Reckless Daughter (1977) and culminating with her tribute to jazz great Charlie Mingus, Mingus, in 1979.

Those albums, although admirable efforts, were difficult to love, and with last year's Wild Things Run Fast Mitchell returned to more conventional, accessible song writing.

The same seems to be true of her performances, and last night's concert was very different from the live material she recorded for 1980's Shadows and Light.

The show, the first popular concert at the new performing arts center on the campus of Community College of the Finger Lakes, started late due to traffic problems that delayed the arrival of the audience. When it did begin, Mitchell opened the show alone, singing Coyote and strumming a hollow-bodied electric guitar.

When she reached the point in the song where the narrator is taken to a road house where "a local band is playing" Mitchell's backup band - drums, guitar, drums, keyboard- joined in.

MITCHELL THEN treated the audience to a superb two-hour show that mixed old favorites- a powerful version of Free Man in Paris- with songs from her album Wild Things Run Fast, such as You Dream Flat Tire, another rocker.

And Mitchell displayed the depth of her talent by occasionally altering the tone of the concert.

There was that old jazz feel to God Must Be A Boogie Man, for example, with anonymous backstage voices supplying the chorus and excellent support from Mitchell's bass player.

The audience cheered when Mitchell sat down at the piano and did a lovely solo rendition of For Free, an old favorite about a street musician who plays the clarinet on a street corner. Later in the concert Mitchell used the piano again for a song from Wild Things Run Fast called Chinese Café.

MITCHELL EVEN brought out a dulcimer-like instrument that she laid across her lap and strummed while singing a song titled Oh Darling, I Could Drink a Case of You and Still Be On My Feet.

She closed the show with Help Me, and although deadline forced me to leave before her encore, there no doubt that Mitchell had brought a superb performance to the new arts center.