Toronto (CP)  For the first time since her career began 15 years ago, Joni Mitchell is a novice at something.

The Canadian-born singer has just finished a three-week stint at home in Los Angeles, polishing a script and preparing for her acting debut.

Mitchell is to appear as a black, male pimp in one of nine short films that form Love, an anthology including work by Lady Antonia Fraser, Edna O'Brien, Liv Ullmann and Mai Zetterling, who directs Mitchell's segment, currently being filmed in Toronto.

Already, her musical background has had an influence on the film, as she insisted on not only being allowed to write her own script, but on preparing the soundtrack herself in advance.

"Musicians are always annoyed at that, that music is always an afterthought in cinema," she said in an interview. "Some people compose fairly articulate scores in a set piece after the fact, but that's not the way I want to work."

Perhaps surprisingly, Mitchell did not write the music. Rather, for the 14 ½-minute segment, she chose a heavy helping of the music of jazz trumpeter Miles Davis.

"My vision of the relationship between the soundtrack and the visuals is very precise. The character I play, for instance, is a Miles Davis fan, and he carries the soundtrack around with him on a big portable cassette."

Actually, Love isn't Mitchell's first involvement with film. She did all the editing for Shadows and Light, a two-hour concert film to which her latest double album is the soundtrack. It is to be aired Feb. 22 on CBS and on pay television in the U.S.

The film and the album feature the corps of musicians she has used since her shift to jazz began a few years ago, culminating in last year's Mingus, a veneration of the late jazz bassist. The change, while it gained Mitchell a new following, also left some old fans behind, and she understands why.

"Friends and loved ones are generally the least supportive of any change," she said. "It threatens the friendship and forces them to change. It scares them, whereas it interests me.

"Look what happened to folk music. When Bobby (Dylan) went electric, some people threw things at him, and those who didn't wept. It made dinosaurs out of them."

Even Mitchell finds some change troublesome, however, and her friend Dylan's latest, well-publicized move, back to the Bible, is one such change.

"I don't think it's a step ahead. I think he's just exploring, but I think it's a step behind.

"He's had more spiritual intelligence before, he's never followed leaders. I've gone through my Christian zealot period, I had an attack of it earlier in my career. I understand the contributing factors to that degree of desperation."