TO GET the most out of Joni Mitchell's songs, I think you must be able to love her a little. The things she sings, and he way she sings them, are so much a part of her, so personal, that objective examination destroys the essence of her appeal.

The effect of her songs depends not so much on any overt statement contained in them, but in the way that her audience reacts to what she says. She acts as kind of a prompt for the imagination of her audience: by being so honest and so direct in what she sings, she acts as a catalyst that sets free the thoughts and emotions of the people who listen. If you can't identify with her songs, if the things she says don't touch off a response in you, her music must become merely an object to be admired from a distance.

But that is not really the point. From that cold point of view there are many other musicians and songwriters to be admired as much, if not more, but when you can feel enough for her to let yourself be as honest and open as she is in her songs, to let her work on your own feelings, she becomes a powerful emotive force.

Her concert at the Festival Hall on Saturday was the first time I had seen her perform, and the only one of her albums I'd heard was "Ladies Of The Canyon", but after half an hour she had created a warm and sympathetic atmosphere with the audience.

She writes with great simplicity, yet after a few numbers I felt I knew exactly what she meant, or rather I knew what her songs meant to me. She didn't have to explain what she said, because either you knew intuitively, or it really wouldn't mean much to you anyway.

Judged coldly, her performance was flawed in places - she had tuning problems, she made a few mistakes, and sometimes when she let her voice fly up it drifted off course - but it didn't matter at all. Joni Mitchell isn't someone you watch coldly, her music is entirely personal and appreciating it is a subjective experience.

The concert was an intimate, friendly occasion. Joni sang and played as if she was at home, and the people clapped, sang "The Circle Game", with her and Willie Nash, and generally joined her in spirit as she sang things like "Chelsea Morning", "Marcie", "Rainy Night House", "Both Sides Now", and some newer things like "Christmas Song".

Her song about a New York street musician, "For Free", comes the nearest of any to be typical. In it, she admires him for playing "real good for free" but doesn't go and do the same, though it obvious she would like to. "I'll play if you've got the money, or if you're a friend to me" she sings. It is a song full on contradictions, without being hypocritical, conscious of her own weaknesses, but accepting it. Joni lays herself open, and then it is up to us.