In her first area appearence in four years, Joni Mitchell proved at the Merriweather Post Pavillion last night that her rare talent is still searching restlessly for new modes of expression.

Drawing on the tuneful structures of her early folk-pop material and the ever shifting harmonics of her later folk-jazz material, Ms. Mitchell and her backing quartet forged a new sound with a bigger rock beat than she's ever used before.

Ms. Mitchell didn't use this new rock approach unvaryingly, but turned to it on certain choruses and songs to drive home her observations about the incompleteness of love and work with a new forceful authority. She alternated reflective folk and jazz passages with the decisive rock passages in a way that made it seem as if confident conclusions were coming out of thoughtful consideration.

Her band was built around the rythym section from her last album, "Wild Things Run Fast." Drummer Vinnie Colaiuta and bassest Larry Klein fueled a propulsive momentum without ever losing the flexibility needed for Ms. Mitchell's gear-shifting songs. Guitarist Micheal Landau was capable of Pat Menthany-like, water color tones on "Coyote" and a Jeff Beck-like screaming solo on "Banquet." Russ Ferrante contributed boogie-woogie piano to "Raised on Robbery" and synthesizer shadows to "Chinese Cafe".

Appearing in a loose black dress with her frizzy blond hair spraying out of a white beret, Ms. Mitchell played sturdy electric rythym guitar for most of the two hour-plus show. She sang with a new, crisp definition that fit the bigger beat, especially when she sang Elvis Presley's "Baby, I Don't Care" and Gladys Knight's "I Heard It Through the Grapevine." Nonetheless, Ms. Mitchell sacrificed none of her customary self-assurance.

Thus even as the band drove hard on a song like "Precious Love" she delivered her sober assessment of love's possibilities with an unassailable imperturbability.

The strongest songs were the newest ones from "Wild Things Run Fast," includng a lovely remembrance of adolescence, "Chinese Cafe" which segued into "Unchained Melody."

Ms. Mitchell proved she could still put across a song without a band. She closed her first set alone at the piano singing a wistful version of "Real Good For Free" and then sang an assertive version of "A Case Of You." She closed the show with just her guitar and a slow, mournful version of "Woodstock."