"I'm a worrier," says Flossie Klotz.

She is sitting on a bench outside the Eisenhower Theater following the curtain on the first act of Tuesday night's preview of "The Little Foxes" -- costumes by Florence Klotz -- and huddling with understudies from the play. She says again that she is nervous. Even though Elizabeth Taylor says, "Her costumes are really wonderful, with a great sense of authenticity." Even though she clutches a newspaper in which a reporter has mentioned that the Klotz costumes got their own round of applause in the pre-Washington run in Fort Lauderdale.

She salves her fears with enormous research on the period costumes she prefers to design. For the turn-of-the-century placing of this show, she has combed her personal library and reviewed several times the Metropolitan Musuem of Art's collection of paintings from that period. Her assistants have done their homework for days at the Lincoln Center library.

Now playwright Lillian Hellman has challenged the authenticity of the men wearing tails in the first act. "But it is just what a nouveau-riche family would wear to impress a businessman coming to dinner in the South at the time," insists Klotz. She has pulled photostats of a film version of the play and, indeed, the men were in tails. But Hellman insists the tails, as well as the lavender lace negligee, are wrong.

As of the time of the preview, Klotz and Hellman had not met. "We'll meet eye-to-eye shortly. We're both the same [short] height so I'm not worried about taking her on," Klotz says, laughing.

Klotz has already made the changes, ordering tuxedo jackets for the men. Monday she fitted Taylor for a new negligee in lavender-pleated chiffon. "If she cares that much, I'll make changes," Klotz says. "As long as it doesn't hurt me."

You touch a sensitive point when you challenge the authenticity of Flossie Klotz's designs. The men's pants have button flies, and the women's dresses have no zippers, either. The men's shirts are cotton and the women's dresses silk, which "doesn't make me a big hit with the wardrobe people," she admits.) Even the jewelry, though fake, was made by a jewelry designer.

With the change from tails to tuxedos, the men wear stiff collars and shirts. The hand-embroidery on some dresses is so fine that it is distinguishable only by the wearer. "It doesn't matter that the audience can't see them," Klotz said. "The actor or actress knows they are there."

The women wear full-length whalebone corsets. These are made by a costume company, since such foundations are not otherwise available. "It helps keep the attitude," sayd Klotz. "Today's kids don't even wear bras. These things make women sit up straight. They handle their bodies in the period of the time." Taylor likes it; she's used to it -- and besides, it gives her a 24-inch waist, says Klotz. ("It even changes the way I sit," says Taylor.)

"I design for the character but keep in mind the body and what would look best on it," says Klotz. She describes Elizabeth Taylor as "buxom with a little waist. An hourglass figure that is perfect for the period." Her olive complexion works well for the colors of the period, too, adds Klotz.

It's only with the lavender color of the negligee -- Taylor's favorite color -- and the star's pumps that Klotz has stepped away from the bounds of the absolutely authentic. "Not everyone wore high-top shoes back then," says Klotz, referring to the slightly jarring stiletto-heel pumps Taylor reveals when she lifts her skirt and train on the stairs of the stage. "It simply makes her [Taylor's] body look better," says Klotz.

Such "poetic license" is less important in movies, where actors and actresses are rarely pictured full length, says Klotz. "When Great Garbo is filmed full length, she's always in bare feet."

During the show's rehearsal period, Klotz insisted the women wear muslin patterns for the costumes so they would get used to walking and turning in their skirts and trains. "Otherwise they rehearse in jeans."

Klotz finds designing for musicals "where the music and dance take over" far less limiting than straight plays. It's musicals where she got her start and for which she has received awards -- Tonys for "Pacific Overtures," "Follies" and "A Little Night Music."

She had graduated from Parsons School of Design, and Brooks Costumes needed someone to paint fabrics. While there, she was asked to assist on the original production of "The King and I." "I thought it was so glamorous. The stars came in for fittings. I didn't smell the greasepaint, but I was hooked."

Klotz first worked with Elizabeth Taylor in the film version of "Night Music." Taylor was so pleased that she asked Klotz to do her wedding costume -- lavender, of course. They met not long ago at the New York opening of "The Mirror Crack'd." "Hey, Flossie, you're doing my clothes for my play," Taylor shouted across the room.

Klotz says she won't stay around beyond the preview performances here: "I've done my job." She'll continue her sleeplessness and nervous eating back in New York.

Just the same, she is thankful for the out-of-town runs. "That's where you get rid of the bumps. And the extra lace. And the tails," she says, laughing.