"Audiences have been great," said singer Joni Mitchell only minutes after she had finished a sold out concert at Merriweather Post Pavilion. "I tell you the letters I get are very encouraging. People say, "We weren't with you three years ago, but now we're behind you."

She no longer is the girlish Joni Mitchell with long, straight blond hair and bangs, a folk heroine of sorts, composer of a generation's theme song, "Woodstock," and spinner of bittersweet tales about herself.

She rose to fame with that Woodstock generation, singing folk songs and ballads with clever lyrics, sometimes with a twist of rock 'n' roll.

But then she went from being a simple acoustic guitar soloist to a singer guitarist with a full band. She experimented with some jazz on her album, "The Hissing of Summer Lawns," She added deep whining electric bass on a later album, "Hejira." The changes alienated some fans, intrigued some new ones.

But she survived those changes and the changes in the musical tastes of the '70s.

Now, just a few months after the release of her most dramatically different album, "Mingus," which is all jazz, she is in the middle of a six week, 25 city tour -- after a three year hiatus. Certainly at the Merriweather Post Pavilian Wednesday and Thursday (the latter date sold out), the crowds were enthusiastic.

Minutes after Thursday night's final encore, a stunning, soulful, even mournful version of "Woodstock," she was guided off stage and into a waiting silver limousine, to be taken to Baltimore Washington International airport and her private Lear jet.

She settles into the back of the car cross legged, and fluffs out her wavy shoulder length hair, the curls now wilted in the humidity. "During 'Raised on Robbery' I felt like that clambake we had for dinner last night," she says, chuckling.

At 35, the on state Joni Mitchell has shed her once tentative, fawn eyed look. It's been replaced by a mellow confidence. Years have softened the angularity of her face. The smile is more sensual. The eyes are a little tired. But the cheekbones, perfectly high and rounded, remain a trademark.

Lean, she wore an orange blouse and black silk pants with black satin high heeled sandals.

"I'm a clothes horse," she said, looking down. "I love fashion. The whole hippie thing was a relief in a way -- we were all so fresh scrubbed and in jeans. I've always enjoyed clothes. But there was an inhibiting time, peer pressure. You couldn't dress up. Well, I succumbed to some of that. If anything I'm coming out now."

Mitchell's "mingus" album combines her lyrics and the music of the great jazz bassist, Charles Mingus, who died in January of Lou Gehrig's disease. Mitchell, at Mingus' request, met with him several times and wrote words to the music.

She spoke almost reverentially of Mingus during the concert. One of her favorite pieces was written for him. a funny song based on part of "God Must be a Boogie Man," Mingus' autobiography.

For her, the collaboration was a meeting of minds. Others feared the worst.

"Well, just the notion of a folk singer flirting with jazz is seen as presumptuous." she said, laughing ruefully, "rather than someone enthusiastically exploring her potential."

"Now, the criticism is lightening up. Even the reviews say that -- that maybe some of the work done a few years ago was taken too harshly. When my engineer and I would work on a project, we'd say, 'Oh, they just don't understand what this is.' Now they do."

She says her audience is "very diverse. Some people like one period and don't like another. After the last two albums I have a small black audience, I have a small jazz audience."

"The tour is a pretty good mixture, mostly from the last five albums," she explained. She opened with "Big Yellow Taxi," but avoided some of the other old favorites. "I'm not looking forward to singing 'Help Me' or 'Both Sides Now,'" she said. Especially 'Both Sides Now.'

"I've heard it too often in supermarkets and elevators. "I guess my first reaction when I hear it is a rush of pride. It's getting universal -- almost to the 'Happy Birthday' stage. But I'm also critical of it when I hear it. They've usually reduced it to the lowest denominator."

Mitchell explained her changes in music as natural, "Most people in the business find a formula and stick to it. I would find that uninteresting."

Her current tour is about half finished. "I just felt like going out," she said with s a shrug and giggle. "I think after this is over I'll go someplace with nice, blue salt water. I'll take a little vacation."

She has a house in Los Angeles and a loft in New York. For the past two years, she said, she has been living with Don Alias, her percussionist on the tour. Alias is a tall, well built man with a warm smile who sits quietly in the back of the limousine with her.

"We've talked about getting married," she said. "I don't know, Kids? I don't know about that either." She smiled softly. "I'm really strong as far as child-bearing goes. But it's a difficult time to bring children in the world." Mitchell was born in Alberta, Canada and raised in Saskatoon, Saskatchewan. She went off to the Alberta College of Art in Calgary for one year, but started singing folk music in coffee houses, and pursued music. She still paints, and some of her albums display her artwork.

"I go on jags," she said. "When I was in a writing block during 'Mingus' I painted 14 canvases. Two are on the album cover. Sometimes I carry a sketchbook. And I've been doing some canvases in my New York loft. I'm always doing some extracurricular art project."

She also knits, and she proudly pulled out a simple, neatly done multicolored sweater. "Everytime I get on a plane now, I take along a bag of colored yarns. I'm making a sweater for Don now."

Mitchell said she enjoys working with the band touring with her -- Alias, noted bassist Jaco Pastorius, Pat Metheny on guitar, Lyles May on keyboard, Michael Brecker on saxophone. "Herbie Hancock had wanted to do it." she said, referring to the jazz pianist who also recorded with her on "Mingus," "but he had his own projects that he had to do."

Her settled feeling about the band is born out of repeated troubles in coordinating her own style with three of the other musicians with whom she has played.

"On this tour I feel like more of a band musician," she said. "I feel like and integral part of the band. They're great musicians and coincidentally, great jazz musicians. But I don't think of our music in terms of jazz or rock or fusion, I just think in terms of 'I wanna hire some musicians to do some work and play some music,'"

Mitchell said she sees her music becoming more rhythmic. "A lot of the older stuff we did tonight was more rhythmic. I would like to go in a more rhythmic direction. I poetry. I see myself going toward epic poems. 'Song for Sharon' was an epic. I tend to think now in longer thoughts. 'Amelia' was an epic, too.

"Musically, I don't know where I'm going. I've flirted with pop classical. Gershwin was kind of my hero in that -- the way he expanded into rhapsodies, but in a pop music context. 'Ludwigs Tune' and 'Down to You' are like that -- pushing the strength of the song into even longer pieces. Some of those songs run 10 minutes long."

Outside the limousine, at the airport, a soft rain began to fall. Mitchell pulled on her shoes.

"I'll know what my next album is as soon as it gets written. It might be acoustic guitar. It might be folk. I never know in advance."

She collected her jacket, knitted sweater and overstuffed purse, and headed for her airplane.