She got started on a dare. Then, for years, the long, leggy woman with the impossibly cavernous smile considered singing a part-time fling. Now that Millie Jackson dominates the blue-read-lewd pop music, she can still take it or leave it.

"This is an industry where you don't have ambitions," said Jackson. "The public will tell you where you are going for the next three or four years. You just say, I hope you will be nice and remember to take me somewhere."

At this moment, the smile was tight, the bluesy voice screechy. "Right now the audience is saying we like this dirty music; keep on giving it to us. When they say they don't like this dirty music, then I will have to stop and say, well, what do you want?"

This laissez-faire, almost fatalistic attitude was the apparent mood of Millie Jackson, 35, successful, and yes, sexcessful, as she breezed through town prior to tonight's concerts at Constitution Hall. A little flippant, slightly testy and totally blase.

This is the downside of a woman whose public image has her dubbed, variously, as the Dear Abby of the Record World, the Richard Pryor of Soul and the Queen of Raunch.

Many of her albums are marketed as wicked wax with labels that boast "X-rated, X-plicit, X-actly." That kind of marketing severely restricts radio air play.But for the last six years, the harder her rap on record, the bigger the sales have been. With almost no air play, her last album, "Live and Uncensored," has reached No. 11 on Record World's rhythm-and-blues charts, and No. 62 with a bullet on its pop charts. Of the 12 albums she has recorded, half have become gold records.

"To be perfectly honest with you," said Jackson. "I never took this serious until three years ago. My contract was up; I renegotiated. And said, 'I am worth this much money? I better start taking it seriously.'"

What actually happened three years ago was the opening of another chapter in modern pop music. Disco, as personified by "Saturday Night Fever" and Donna Summer, was as hot and diffuse as a strobe light. And the debate about its lack of substance was just as loud as its product. For certain people, Millie Jackson filled a void. She talked, she rapped, just like B.B. King and Issac Hayes had done with smaller, pre-crossover audiences. What she sang wasn't that much different from what Bessie Smith had suggested 60 years ago.

But the times benefited Jackson. She took the lingo of the soap opera to a very explicit level. She translated musically what writers Ntozake Shange and Michele Wallace were saying in profitable plays and books about the hardships of black men and women.

And like the other liberated voices of the 1970s, what she describes is occasionally another perpetuation of the myth that the black woman is a bitch, a tart-tongued harasser of her man.

She declined to discuss just where she fits. "I like to think about myself as an entertainer, period," she said. "Now where you put me, that's for you to decide.

"I'm different because of the way I say things. It's like saying, shall we have intercourse tonight, or shall we hit the hay? Or saying to a girlfriend, shall we go out and get some this evening?"

Though she professes not to care about categorization, don't mention Jackson and Summer in the same breath.

"The only time I get upset is when people keep saying, 'Miss Summer, can I have your autograph?' Yes, everytime I change my hair, she changes hers," said Jackson.

And she turns from simmer to boil when asked whether Summer's success has influenced her style. "I don't give a darn about her success, one way or another," said Jackson. "We are in two different fields. I just wish she wouldn't look like me. And she doesn't really, but when people see her on TV . . . they don't know she's short, she has a wide can, has crooked teeth on the bottom. They don't realize I am the one with the narrow a-- and the straight caps."

This catty patter is part of the current packaging, but Millie Jackson wasn't always so wild or so packaged. Back in Thomson, Ga., where she was raised by her grandparents, Jackson had a six-days-a-week-in-church upbringing.

"I can relate to Dinah Washington," she said, discussing early influences.

"And Gladys Knight, Otis Redding, Sam Cooke, Mavis Staples. I like what they were doing . . . the gusto."

With that basic blues in her blood, she moved to New Jersey when she was 15 and was reunited with her father. After high school she got a job pushing the coffee wagon at Schrafft's. "I didn't have any ambitions, just paying the rent. I was making more money than most of the people I know in my category at that time," she recalled.

One night at the Palm Cafe in Harlem, this ordinary life took a new turn.

At the rambunctious urging of a friend, she joined the band. "There was a man in the audience giving a show the next week at the Chrystal Ballroom; he liked me and hired me. Someone saw me there, liked me and hired me for three weeks at the Zanzibar in Hoboken. Then someone liked me there and hired me to do the 521 in Brooklyn," she said, racing through the litany.

For a while this string of club dates was "just extra money in my pocket, no big deal." But in 1967 she quit Schrafft's and went on the road. The life of Elks clubs, Booker T. Washington gymnasiums and Greater Bounty church basements didn't make the singing life appealing.

Two years later she quit traveling, got a daytime job in Kimberly Knitwear's stockroom and nighttime gigs at clubs around New York. "I did my first record during that period, called, 'A Little Bit of Something,' and it sold even less."

When her career started perking, she took a leave of absence from the shipping department. "I always thought the next record wouldn't be a hit, so I can go back to work. My whole career has been doing something I liked that I thought would end soon and didn't," she said.

Right around this time she had a brief marriage. "He didn't understand I was two people, Millie and Mildred," she said. "Millie is the workaholic, go get the money. Mildred is the one who goes home and plays with the kids. They don't have different ambitions, because without Millie, Mildred is going to starve to death. And without Mildred, someone is going to kill Millie."

The singer has found peace between the two and neatly incorporates the lives of her two children, Neisha, 13, and Jerroll, 3, both born while she was single, into a happy existence in Teaneck, N.J.

By 1974, Jackson had convinced her managers that she couldn't be "a nice, little, sweet Diana Ross the Second," and that the raunch that worked in her concerts could translate to recordings. This candidness earned her a Grammy nomination in 1974 for best female rhythm-and-blues vocalist for "If Loving You Is Wrong" and a host of groupies.

What she didn't anticipate was her role as a confidante to her fans. "People started coming up, saying, 'I am going with a married man; what should I do?' I said, 'What? Who are you asking?' Actually, it was funny. I had to say to myself, people are really asking me this, huh, no kidding."

Occasionally she feels her imagemakers have gone too far. On the "Live and Uncensored" album is a sticker warning that the material is for 'mature audiences,' bait to her fans but a red flag to radio programmers. No one consulted her.

"I didn't realize that until I was in Florida," she recalled. "I said, who put this s--- on my album? I was crazy. I don't think the album is X. In order for it to be X, I would have to have an orgasm on the record and you would have to see it. It wasn't the image I was worried about. I felt it wasn't truthful.

Her audiences, says Jackson, are mainly the housebound, the women who will recognize the soap-opera innuendo in "All the Way Lover," and other songs. "Most of the [professional women] detest me. I represent something they want to forget. Because they have been brainwashed into thinking, 'I have to be someone else to get ahead. This woman represents what I used to be and I don't want to be bothered by this,'" she explained. Her press agent interrupted to tell about a television publicist who told him she hated Jackson and used to buy her records to have "melting parties."

Jackson looks unperturbed, shaking a cascade of waves, as she listens. Her reaction is loud, crackling. "She bought the album, didn't she? Who gives a s---!"