Over the last 10 years, British singer-songwriter Joan Armatrading has amassed so many glowing reviews that her record company must have thought about calling in an acclaim adjuster.

Still, she remains an unheard mystery to most Americans, who have avoided her sophisticated and superbly tailored music as if it were the "avant-garde." As a result, Armatrading has steadily increased the rock quotient of her albums; at Constitution Hall on Wednesday night, she almost knocked down the walls with a set laden with emotional resonance and electric eclecticism.

"I just want the music to reach a whole lot of people," Armatrading said earlier in the day. "When I first came to America 10 years ago, I played a whole lot of clubs. I'd hate 10 years on to be doing a gig in a club for 200 people. I wouldn't bother, what's the point? If you start out sweeping the office floor, when you collect your pension, you don't want to still be sweeping the office floor. You should either be sitting at a desk, managing it or owning the blooming place. It's just job satisfaction."

Born in the West Indies but living in England for most of her 31 years, Armatrading is in many ways an odd-woman-out in a business that thrives on commonness. She is a black female whose original music transcends traditional boundaries; one hears echoes of jazz, folk, rock, reggae, blues, pop and gospel, all of which dissolve and emerge in a throughly unique maelstrom of forceful rhythms and intriguing lyrics. Her music--which shares an ecstatic tension with the work of Van Morrison, Joni Mitchell and Nina Simone-- tends to melt hearts and recast them in a wider consciousness.

Over the course of nine albums, Armatrading the artist has managed to bury the "very hidden, private person." She still tends to regard interviews as cross-examinations and has earned a nickname from the British music press, "Joan Armorplating," to suggest that impenetrability. In recent years, just as her music has become commercially acceptable without conceding its humanist heart, Armatrading has started to match the confidence deployed on stage with an openness offstage--with reservations. She always wears the key to her London flat on a chain around her neck, but there's the certain knowledge that only she's allowed to care what goes on behind closed doors.

"Everybody has a right to the privacy they want for themselves," she insists. "You have to give a certain amount away, to do with your writing and where you're going, stuff like that, but sometimes people take it further and try to get into real personal stuff. Every single question that you're asked you don't have to give an answer to. That's just a matter of you being a human being."

Armatrading's history has been constructed in bits and pieces. She picked the guitar up at 14, teaching herself to play it and the piano; her father hid his guitar to discourage her musical interests, but Armatrading got one by trading two baby carriages at a Birmingham pawn shop. Her first appearances were in folk clubs singing Paul Simon and Bob Dylan songs. At 18, she accompanied a friend to an audition for the British company of "Hair"; the producer passed on the friend but picked Armatrading out of the audience; in an 18-month run, she was the only person in the cast who never took her clothes off.

Armatrading's very first album earned critical kudos, revealing a commanding singer capable of hot flashes and cold burns and a thoroughly eclectic songwriter capable of revealing a wide range of emotions. Unfortunately, Armatrading developed a cult rather than a mass following, a barrier that she still struggles with. The cult has managed to grow in gimpy leaps and half-steps, but stateside it became a question of whether she would break in America or America would break her.

She's been fortunate in having a record company (A&M) that apparently believes in her enough to mount a national campaign to "Free Joan Armatrading." "She's not a black act/ she's not a white act/ she's not a jazz act/ she's not a dance act/ she's a class act," go the spots, which then berate radio for shutting her out and offer a free sampler of older material with a copy of her new "Walk Under Ladders." It's the kind of push that could--and has--backfired on less deserving artists, but Armatrading is thoroughly unembarrassed. "It's their idea. They're just trying to get people who haven't heard myself on the radio to go in the record shops."

In England, Armatrading is a major star. Her albums sell extremely well. Bob Dylan specifically asked for her as an opening act when he played before 280,000 people at the Blackbush Festival. Last year, the British music press voted her stage show the second most exciting, behind Bruce Springsteen's. That show, like her three most recent albums, has become both harder (in the rock sense) and happier (in nuance). As part of her new image, Armatrading has taken to writing her songs on electric guitar and, most recently, on synthesizer ("great for giving you ideas, but you have to develop them").

This tour of America has been her most successful ever, a string of sell-outs that suggest she may soon give up her title as "rock's best kept secret." Armatrading is beginning to shed another burden, that of a feminist writer. "I write songs for anybody that wants them," she insists. "If a gay person wants it, it's theirs. If a feminist wants it--or a man, a little boy of 10 or somebody who's 60--it's theirs. I didn't write it and say 'Well, only women can listen to this, or only people under 30.'

"The songs are for everybody. I don't get involved in movements. You shouldn't limit things. I don't want to be just playing to 10 people. I want to play to as many people as I can possibly get to."