IF CHUCK MITCHELL is known in Toronto at all, most likely it's as the husband of Joni (Anderson) Mitchell. Or maybe a few remember him from a brief appearance at the Penny Farthing about two years ago.

But after his week at the Seven of Clubs where he opened last night, Toronto, at least, should have discovered his tremendous talent - talent that is as varied as the songs he sings and as abundant as his voice is deep and rangy.

Chuck Mitchell isn't just an ordinary folksinger. An intelligent performer, possessing a really fine voice which he can control, he is one of those rare singers whose sense of the drama of music extends into the drama of the theatre.

Add a dash of stage personality and you get the epitome of the good cabaret performer and potential concert artist.

That's what he and his wife (who opens tonight at the Riverboat) would eventually like to move into - "the cabaret-type thing, not the typical folkmusic show where you can't really work on everything. We're looking toward a thing that would provide more avenues than we now have."

Chuck Mitchell's sensitive use of music and drama make him one of the few performers ideally suited to performing the songs of Brecht and Weill, without losing their very clear sense of theatre. Along with Martha Schlamme, he is thus one of the even fewer number of singers who are able to do this music well (Lotte Lenya and Will Holt, the most notable Brecht-Weillians, were primarily stage actors).

And on top of his excellence in Weill's Brandy Merchant Song and Mandalay Song, he did such diverse tunes as Have Some Madeira, My Dear, Flanders and Swann's the Gnu Song, Soon It's Gonna Rain from the Fantasticks, and Eric Andersen's Broken-Hearted Mama.

But the best thing he did all night was Dino Valenti's Get Together, one of the most beautiful, most meaningful songs of the past year. He did it down-tempo and subdued, stronger than the strongest prison wall.