The door to the darkened hotel room opens and Chaka Khan comes in, soft as a shadow, with a shadow's soft silhouette. Dark brown, billowing hair shades into a black velvet coat, and the folds of her loose black blouse settle, as she sits down, over a rounding belly. Chaka Khan is five months' pregnant.

There has been, by necessity then, a certain softening of her image on this five-week tour, her first solo tour since she left Rufus, the group that pole-vaulted her from obscurity.

The old image was never very hard to figure, at least visually - feathers and leather and halter tops, bras connected by little more than imagination to bikinis cut high on the hips, a mouth that defined desire, movements that defied gravity, cat's eyes, long and smoky, that could narrow in a moment to the thin line that divides temptation from surrender.

Actually, she says, it was practicality that engendered the costumes, not the aura of rampant sexuality that seems somehow to have attached itself to her growing reputation.

"I designed them," she says, "for the purpose of mobility and so I wouldn't get too hot on stage. It just happened to work out that the bra is the closest to comfortable that a woman can get and still be dressed," and, as for the leather, "it was original at the time; no one else was using it."

Besides, she ways, "It saves all that time and money taking silks and satins to the cleaners." Chaka Khan could probably keep a straight face holding a royal flush.

Still, sitting there, as the afternoon slips quietly toward her evening concert at Constitution Hall, she seems at odds with the flamboyant persona splashed so lavishly across the cover of Record World and Soul, the articles in Jet, and Circus.

Her first solo album, released in October, is about to go platinum - a million copies sold. Her current tour will take her to 19 dates in 15 cities.

Her first solo single, "I'm Every Woman," was produced by Arif Mardin, a singal in the music industry that Chaka Khan has been singled out by those who place the chips in that world for the push to a position among the superstars of female vocialists, like Diana Ross, Natalie Cole, Aretha Franklin.

She is 25 now, the fame and money came at 20, and at the time, it was a little too hot to handle. Now she speaks in muted tones, with a measured forth-rightness that comes from learning late what happens when actions and words aren't weighted carefully.

"I spent a lot of money recklessly," she says of that first sudden rush of stardom, and she found herself at the center of a raft of rumors - about her personal life, about her alleged drugtaking habits, that were "pretty much not the truth. It seemed that if I experienced life, everybody had to know about it. If I had been working a Sears store, doing the same things, no one would have said anything."

The pace on stage was fast, she says, and so offstage, "I guess I was unwinding at a rate faster than most people." Now, she says, "I haven't necessarily toned down what I do, but I keep it among just a few good friends. Privacy is a sacred thing in a way."

So she lives on a ranch in Malibu with her 5-year-old daughter Millim (by her former marriage) and her songwriter-band manager husband, Richard Holland. "I'm too wild," she says. "I need a marriage band on my finger. At least I know that about myself. A lot of people never figure it out."

She grew up Yvette Marie Stevens, a middle-class Chicago kid, Catholic family, Catholic school. She fought against that background, took the name Chaka Adunne Aduffe Yemoha Hodarhi Karifi and left home at 16 to find her way in the hard world of North Side Chicago nightclubs in the late '60s and early '70s.

"It was really rough," she says. "It took a lot of peppermint schnapps and other things to get through it. There were lot of us - eight or nine people - living together as a family, working at night, living on welfare, stealing money - pretty much of a vagabond existence."

Then Rufus came along, five musicans in need of a female singer, and off they went to Hollywood in 1973 to become famous together, until this year, when Caka Khan went off to be famous on her own. She still owes Rufus two more records but all the personal appearances, all the promotion are hers. Alone. It can be a little nervewracking.

"The audience comes to be manipulated," she says. "They want to be charmed, and talked to. I'm not very good at it yet, actually. I don't know what to say. I'm better with the hecklers - at least I'm getting some response to what I'm saying."

She has been compared to Donna Summer, queen of sex and disco. She knows what to say to that. "The only thing Donna Summer and I have in common," says Chaka Khan, "is that we both know how to speak a little German."