Cher's navel, Raquel Welch's bosom, Diana Ross' body -- for Bob Mackie, they're all in a day's work.

There are no more than a dozen designers in demand for the cream of the costume jobs for film, television, theater and special appearances. And Mackie heads this very small list -- especially when it comes to glamor clothes. No wonder: In less than 20 years, he has won four Emmy Awards, two Oscars nominations, and designed for stars from Mitzi Gaynor to Toni Tennille.

His is not the usual fashion designer's challenge of making ordinary women look as good as possible. Mackie starts with extraordinary figures, including Ann-Margret, Cheryl Ladd, Marie Osmond and Carol Burnett, and succeeds in making then look better.

Gilding the lily, you could call it.

In town to lead off the Smithsonian's lecture series on Costume Design that begins this evening, the 40-year-old designer recalled some of the special problems -- and specific remedies -- he has encountered in making his clients unforgettable.

The problem with Cher, he says, is that she often tries to make the navel cut-outs or bare-midriff styles more revealing. So Mackie has to put special construction into some costumes so that cher can't change the shape.

"From her navel to her crotch the lady is so long that the space before you get in trouble you just don't believe," says Mackie. "Sometimes I attach the dress in back so that she can't pull it down," he says. When he gives into her requests to make a garment more revealing, he always regrest if after.

He also insists that Cher wear a bra on television. She does, but Mackie says, "she doesn't like it much. She says it simply is uncomfortable."

Cher gets so comfortable in her costumes, whatever they are, that she stands like she is wearing a T-shirt and jeans, and he says: "You have to make sure there is plenty flapping around between the legs."

For the reason he won't design front slits for Cher, and only does them occassionally for Bette Midler, when she wants to look "cheesy." But, he says, a slit that comes up on top of the leg is always more flatterning.

For Carol Burnett you have to put pockets in everything to make her feel comfortable."She has more pockets in beaded dresses than anyone I know," he says.

"No pockets for Raquel Welch," he laughs. "She started selling her 'visuals' early and she knows them inside and out." For Welch nothing is changed. The only effort is to show it off in the best possible way, occasionally with one layer of chiffon and just a few beads.

With Mama Cass, "I just ignored the fact that she was fat . . . she was so large I couldn't do anything else." Once he dressed her as a Mae West, another time as a gypsy.

In his new book, "Dressing for Glamour," which harps on many "don'ts" as a way to discern what is best to "do" about clothes, Mackie points out that most heavy women wear their clothes too tight, thinking that wearing a smaller size makes the look smaller.It doesn't. And big caftans often make big women look bigger still, he says.

Beyond beads, feathers, plunging necklines and body-clinging silhouettes, Mackie admits using toupee tape and surgical adhesive to keep things in place when necessary. He invented shadow seaming, a trick he believes even Paris couturiers don't bother with, to camouflage the seams on a white dress.

It's like "packaging a product," he says. While some insist that he "made" Cher with her costumes, he says "The woman brings a lot to it. Put someone else in those clothes and you'd be in big trouble."

When he's called in to create clothes he charges both a consulting fee and the cost of the clothes . . . figured, for the workmanship at $15 to $16 an hour, so that "nothing costs less than a couple a thousand dollars." The most expensive garment was the $30,000 creation he made for Diana Ross that was embellished with fur.

Many of the stars he started working with as guests on the Carol Burnett show. Mitzi Gaynor was the first lady to trust me to do her clothes," says Mackie. "Burnett came to see the act and hired me for the show. Then Cher was a guest on her show," and so it has gone.

Ocassionally he has shaped the character as well as the costumes.Burnett's Mrs. Wiggins, the secretary who watches the clock and files her nails, was in the original script as a mature character. "Carol had done a lot of old ladies," says Mackie. "So I called her up and suggested a different slant." Once Burnett approved, he designed a skirt so tight that it gave Mrs. Wiggins her funny walk.

Carol Burnett said of the design: "That skirt should be featured in Architectural digest."

His parents were separated, and he was brought up by a grandmother who was perfectly happy to have him industriously making up costumes and creating sets on his bureau top as it kept him quiet and out of her hair.

He saw his designs made into clothes for the first time in high school, where he also acted in school plays.

Studying at Chouinard Art Institute in the late 1950s, he was put in charge of costumes for the Art Students ball, particularly the queen -- sex symbol Jayne Mansfield -- and her court. "The project became an engineering as much as a design feat. I labored for hours in order to be able to cantilever the queen's bust as far out as it would go, wile slitting the sides of both legs, also as far as possible," he says in his book.

In the early '60s, he worked on sketches for Glenn Ford, Charles Boyer, Hope Lange and Marilyn Monroe -- all from the back room, where he never got a glimpse of the actual personalities.He went on to work for Edith Head, and when Carol Burnett came to the studio for her first film, they wouldn't let Mackie near her. The role called for tailored suits and he was already established as a glamor designer.

In 1963, he switched to television costume designing as Hollywood glamor films started to diminsh. He was Ray Qaghayan's assistant on the Judy Garland show, doing all the guest and chorus clothes.

Mackie is also interested in commercial fashion. And not just because of his won line on lingerie for Glydons at Woodies, which he is promoting (along with his book) while in Washington. He has to worry about current trends because his audiences have to identify with his costumes.

But his only real problem now is that some of the sure-fired techniques that he uses for looks for sexy to trashy Including beads, feathers and slits) are now on the racks of department stores. "Bette Midler told me I can't do corselets or garters or corsets or tights anymore because straight girls are running around looking that way," he says.

Even Cher has noticed it, he says. She said to him the other day, he reports, "Look at all that stuff we used to do for fun. Now everyone is wearing it out on the street."