This woman with the gentle gray-blue eyes, sitting demurely in the sunny hotel room with a tissue-soft, everything'll-turn-out-fine demeanor, is Barbara Cook. The same singer who starred in the original Broadway productions as Cunegonde in Bernstein's "Candide" and Marian the Librarian in "The Music Man" (for which she won a Tony), and performed other roles in such biggie revivals as "Any Wednesday," "Showboat," "Carousel" and "The King and I," not forgetting innumerable singing triumphs at such venues as Carnegie Hall. But on this sunny October afternoon all the stellar careers in the world can't stop her back from aching.

"It's the rack," she says, referring to the slight slope of the stage at Ford's Theatre. "Imagine you are trying to cavort around and dance for two hours on a hill, instead of a flat surface."

A fine way to feel on the eve of a two-week showcase at Ford's that opened Wednesday. Called "A Broadway Evening," the evening features Cook as actress, comedian and -- what she is most known and loved for -- musical performer. But last week's preview performance, which was greeted with a standing ovation, has left her spine out of whack this afternoon.

Her stage action in "Broadway" is -- unfortunately for her back -- anything but sedentary. The show is filled with theatrics. In addition to singing a familiar selection of Berlin, Gershwin and Willson, Cook performs some torchy vamp and burlesque numbers; tap-dances a whimsical routine with backup singers Julie Nicholas, Sheilah Glover and Willow Wray; and, among other things, plays a broad comic sketch as an aged eccentric waiting at a bus stop, tacky plastic shopping bag and camera in tow. It's not your average chanteuse-by-the-piano evening. But then, Cook isn't your average chanteuse.

"We wanted to try and find some way to really make the evening a more theatrical evening rather than just a recital of songs or recitation of my career . . . to try and take it somewhat out of the style of a concert. So that then people would feel they had seen something that really belonged in a Broadway theater. That's what we're aiming for."

Cook fans will find out a little more about the singer in a Cook-created song medley called "Moving Picture Vamp" in which she reminisces about her Atlanta childhood, with such high points in her Hollywood-struck life as the world premiere of "Gone With the Wind," where she watched such screen royalty as Clark Gable, Vivien Leigh, Laurence Olivier and other glitterati breeze into the theater.

"When the MGM lion would come on the screen," she says with a juvenile sincerity, "I'd start salivating . . .

"It's all true," she says of the stage reminiscences. "All of those things happened to me . . . I loved movies, oh my God. Jeanette MacDonald and Nelson Eddy -- I was craaazy about them. And Judy and Mickey. Ann Miller. All those people . . . This is a little more autobiographical than I had planned on. I tried to think of them as just reminiscences, rather than 'And then I did and then I did . . . ' I think of them as anecdotal. Little things I hope people will find interesting -- to join the songs together.

"Sometimes I think it's amazing that I ever got into this business, because I was a very frightened, nervous person. I was very unsure of myself. It amazes me that I did persevere."

Persevere she did, however. When she was 20, Cook went with her mother on a visit to New York. "I wanted to go to New York so badly . . . I wanted to do musical comedy, I wanted to do musical theater. And I didn't even really know what musical theater was." It was ostensibly to be a two-week visit but "I packed up everything I owned. I think she didn't believe me. I was really serious about it. And then there I was saying goodbye to her and she was on the train to Atlanta."

Settling in the city in 1948, Cook later obtained an agent and three years later was given the part of the inge'nue in Fain and Harburg's "Flahooley" on Broadway. "I think it was because I was driven," she says, with anything but a driven look in her soft gaze. "I wanted so much to do what I do that the desire was greater than the fear . . . I wasn't seeking fame. I was seeking to communicate. I wasn't seeking a career. I just wanted to sing and perform and get through to people."

Then followed a 20-year chunk of credits -- musical and straight drama -- on Broadway and other New York stages. " 'The Music Man' was the biggest hit that I did and 'Candide' was the most prestigious and most difficult by far."

But with the roles came ups and downs that apparently go with stage life. They have been well documented: The 13-year marriage that ended in divorce in 1965 (from which she has a son, Adam); and Cook's discovery that certain unexplained mood swings and weight gain had been due to hypoglycemia.

She undertook a diet regimen to counteract the problem and embarked on a "second" career in more intimate nightclubs and small halls, including a summer tour in 1973 singing Gershwin. In 1975, her first Carnegie Hall concert garnered critical raves and led The New York Times to declare there was "no other voice of such magnificence in popular music" and call her "an instant cult figure." She appeared in Washington several times, looking trimmer and more assured each visit as she played to sellout audiences.

As for her audiences, Cook has a particular fondness for the Washington cult contingent: "They're very alert and bright and really quick on the uptake. It's somewhat like performing for a college audience -- they're right there, they get it . . . I performed several times at the Kennedy Center but mainly I've performed at Charlie's and it's just a very intelligent, bright audience . . .

(On stage in "Broadway," stressing her love of Washington and, particularly, shopping in Washington, she states, "Hell, I'd crawl on my hands and knees to Neiman-Marcus.")

"I love it when young people come up to me and say, 'Boy I never heard you before, my friend told me you were great and I had to be dragged here and I'm glad I came,' and that sort of thing. It's kinda nice.

"There's a physician that's a friend of mine now who went to Paris to see me and he just went to Chicago to see me. He flies all over. Very nice guy."

At 57, Cook feels no impulse to stop. Her voice, she points out, is not that of an opera singer's where long-term strain takes its toll. "I think I'm singing now as well or better than I ever have . . . People's voices do change as you get older. I think my voice is warmer and richer than it used to be. I kind of like it more. There was a lightness about my voice before that I think is changing into a more mellow sound, but I kind of like it."

The "Broadway" venture is a bid for the real Broadway, she says. The show is undergoing continual changes as the ensemble, which also features musical veteran Wally Harper (Cook's music director/pianist of 11 years), alters the dynamics and even changes the songs to its satisfaction. "I'd say maybe half of the show has changed or a third," says Cook, comparing the Ford's Theatre program with the prior version in Chicago. "We're putting things in different places, covering new songs."

After Washington, "Broadway" will continue in Boston and in a yet-to-be determined number of additional cities: "We've talked about Phoenix and Tucson and San Diego, San Francisco. We've talked about several places . . . We'll see what happens with this show but I would like to do another book show after this -- a show that has a story, a musical comedy."

She will continue to sing her favorite type of song, she says -- "the more emotional ones. Those are the songs that I lean toward always, and that I enjoy doing, especially the simple emotional statements."

And she will sing, she emphasizes, "till they drag me off. I show no signs of flagging at the moment and I don't want to stop anytime soon, I can tell you that."