LOS ANGELES - Skepticism is almost automatic when you hear of a project such as "Starart," a hardcover book heralded by the local art exhibition of six popular musicians. It seems a crass cash-in on their musical popularity - i.e., "If you like Joni Mitchell's records, you'll just LOVE her paintings …"

But the Starart project bears closer scrutiny for a few reasons. The most important one is that some of the works are impressive - not brilliant, but infinitely beyond proficient. Another is that these artists do not have to rely on their art for money and are thus perhaps more frank in appraising their works - ego apparently is not as crucial when one's livelihood is not involved.

The musicians involved in the project are Joni Mitchell, John Mayall, Cat Stevens, Klaus Voormann, Ron Wood and George Frayne, better known as "Commander Cody." All but the latter two have exhibited their work on album covers - a neat and natural juxtaposition of their talents. In fact, Voorman's cover for the "Starart" book is reminiscent of his famous cover for the Beatles' "Revolver" album.

"People usually think that I paint to escape from the tension and pressure of being on the road," said Frayne at the casual, star-studded exhibit opening. "But, au contraire - that couldn't be farther from the truth. I'm as intense about painting as I am about my music."

Joni Mitchell sees synchronous influences on her art and music. "When I used to sing and play simple songs in coffeehouses," she said, peering intently through a fringe of blonde curls, "I made simple line drawings. But as I went into musical layering, my drawings went along. Any time there was an aesthetic shift in one, the partner would follow suit."

Her felt-tip drawings from the late '60s and early '70s are delightful, especially ones such as "Table Laurel Canyon I" and "II." The difference between those works and her later ones may be her efforts to interpret photographs. She seems to be a more expressive artist when she is working from life. Her pure abstractions are dreary, but her works influenced by the Southwestern palette and the purity of Georgie O'Keeffe are quite lovely.

Mitchell seems very confident in her abilities, possibly because her art has quite a bit of exposire. Yet Klaus Voormann, who has probably achieved more notoriety (to the general public) as an artist than as a studio bassist for John Lennon, Carly Simon and Harry Nilsson, is more tentative on discussion of his work.

"Playing a lot of music can take you away from being able to draw," he said in a soft voice still tinged with the accent of his native Germany. "The expressions are so different - even though they are both expressions of self.

"The mediums of art and music are very separate, I think. A profound experience would influence both, but I don't think they influence each other.

"Every one of us (the six artists) shows weaknesses. For me, I have problems with techniques because I have never really had the time to learn to use oils properly. The book is an honest sort of statement and doesn't make every one of us look like a fantastic painter, but it does include some very revealing statements."

Ron Wood is perhaps the biggest surprise, because his flaming lifestyle and image just aren't consistent with exacting art. He is a sketcher, with felt pen or colored pencil, and his work is very precise. Like Mitchell, he is far better when he works from life than when he draws from a photograph. He is best in capturing a mood or expression, evident in a felt-pen drawing of fellow Rolling Stone Keith Richard last year or of the color pencil sketch of John Belushi.

When asked about the relationship of his art and music, Wood approached the subject from a monetary standpoint. "It took one to get the other on the road," he said. "I tried and tried with the art but I realized that $8 a week wouldn't do."

John Mayall approached his two interests the opposite way: Mayall never thought he could make a living playing blues, so he became a commercial artist. When popular taste evolved to include blues, Mayall made the switch. He makes little distinction between art and music, claiming they are both creative outlets and essentially the same to him.