ONLY 15 years ago, mezzo-soprano Frederica Von Stade was a salesgirl at Tiffany's. Now -- quite famous at 34 and here to sing in the opening of the Kennedy Center opera season -- she sinks her demure, stylish form into an overstuffed sofa in Washington, quietly lamenting the passage of years and reflecting on the joys of her Georgetown childhood.

"You come back here and Georgetown doesn't seem to change that much, except that it is more chic. Down on Wisconsin the Georgetown Theater, where my older brother and I used to drop cherry bombs, is still open. And we're staying near the playground at Volta and 34th, where we used to play, and it really is the same, except that the tennis courts are better.

"And the streetcar tracks are still there, but not the streetcars. Was it 25 years ago that that happened? Oh, my, it's horrible to be old enough to be thinking in clumps of 25 years."

Ten years ago Von Stade made her first tentative move toward celebrity with her debut at the Metropolitan Opera in what she calls a "one-liner" role in Mozart's "The Magic Flute." Four years later, she was making her first Washington operatic appearance in the major role of Dorabella in Mozart's "Cosi fan tutte."

But up to the time of the Met debut, the young woman from Georgetown was a self-effacing music student who "loved music but never expected even to sing professionally" when Sebastian Engelberg, her teacher at Manhattan's Mannes School of Music, persuaded her to participate in the annual Metropolitan auditions.

She was only about five years out of high school and had wandered from job to job in Paris and in New York when she won the auditions. Since then, she has risen to become one of the leading mezzos of her generation, second to none of her more senior colleagues -- including Teresa Berganza, Christa Ludwig, Tatiana Troyanos, Elena Obraztsova and Marilyn Horne.

The extent of her reputation first became clear here when she came back to Washington in fall of 1976 -- singing, within a matter of weeks, with both La Scala in Rossini's "La Cenerentola" under Abbado and the Paris Opera in Mozart's "The Marriage of Figaro" under Solti. Now she returns to sing, with the Washington Opera, in the first American revival in many decades of Massenet's neglected "Cendrillon".

"Cenerentola" and "Cendrillon" make two Cinderellas for Von Stade and Washington. And in the three years between, her personal road to success and happiness has been considerably simpler than that of her storybook counterpart. There is little sign of the stereotypical neurotic balancing act between demanding career and possessive personal life that plagues many jet-setting singers. She argues that, in fact, her personal life makes the career easier, particularly her relationship with Jennie, her 2-year-old daughter. "You walk in the door after a performance with your mind all tied up about the high note that didn't go just right, and before long, you're wrapped up with the child instead. They're so absorbing you forget the rest."

Her closest teacher is her husband, baritone Peter Elkus. They got to know each other in the late '60s while studying at Mannes under Engleberg. Elkus' subsequent career has been concentrated mostly in teaching. This year husband, wife and child have traveled together as Von Stade has gone from engagement to engagement, and the family is here now. "Right now we don't have a home, but Paris continues to be our base. And we will be settling there," Von Stade explains.

To some extent Elkus has curtailed his career to clear the way for Von Stade's. Working with a spouse, she says, is "an enormous help for a singer because Peter always understands what I am trying to go for and can tell me if I am doing it. And also he can stay there and be supportive. It's a wonderful gift, having an ear like his. Peter goes through all the tension with me, but doesn't get the thrill of being on the stage. But, for the present anyway, Peter seems satisfied."

Without the support of her husband and the encouragement of Engleberg, who recently died, Von Stade might well never have become a singer. "I originally went to the Mannes school because I could't read music. I was doing 'industrials' then. That's where you put on a product-related show for a business gathering. And I was hamstrung because it was difficult to learn music blind." Asked when it first dawned on her that she had the potential for a major career, she replied, "It's still a surprise. I just never went through that step."

To counter the culture shock that might have resulted from such a rapid rise, she took a year off two years ago, which gave her time to make many of the recordings now arriving on the market -- and to have a child as well. Also she plans to limit her schedule as Jennie becomes old enough for pre-kindergarten in about a year and a half. "I have to be with her during the school years," Von Stade says.

This concern for Jennie above all else is reflected even in the way the child came to be named. Von Stade had become enamored of the beguiling Carol Hall song "Jennie Hall," popularized by Barbra Streisand, which begins: Jennie Rebecca, four days old, How do you like the world so far? Jennie Rebecca, four days old, What a lucky, lucky, lucky, lucky girl you are.

Forty-eight hours after Von Stade recorded the music -- on a recital disc for Columbia -- her daughter was born. And she was named Jennie Rebecca. Since then Von Stade recitals have regularly closed with "Jennie Rebecca."

A cheerful and poised individual, Von Stade was once aptly described as looking more like "a young, well-heeled member of the Metropolitan Opera Guild than a stellar member of the Metropolitan Opera company." She makes no effort to refute this:

"I wouldn't say that there haven't been some difficult moments, but I've been awfully lucky and things have come easily. For instance, there just happened to be three major new 'Marriage of Figaro' productions coming along in the mid-'70s -- in Paris, Glyndebourne and Salzburg -- which was the right time for me because I am a Mozart singer. What if that had been the year for 'Tristan' instead? I would have been lost. Likewise, the French operas are getting revived now, and they have some roles that lie well for my voice, like 'Cendrillon.'"

That voice, which she lists as a "lyric mezzo-soprano," does not lend itself to easy categorization. It is lighter than many mezzos, and darker than many lyric sopranos. And she can reach all the notes in either category. As a result, she recently recorded Melisande in Debussy's "Pelleas and Melisande" with Herbert von Karajan -- a role customarily sung by sopranos. Likewise, she has recorded the soprano last movement of Mahler's 4th Symphony with Abbado -- a part that her friend Kiri Te Kanawa, with a notably higher voice, sang here earlier this year under Abbado (Von Stade interjects that Te Kanawa's voice "is one of the most beautiful that ever was"). She even mentions the possibility of doing Mimi in Puccini's "La Boheme," but then backs away from it.

Because Von Stade's voice lies right on the edge between mezzo and soprano, she has to choose her roles "by testing. And the issue is not, 'Can I handle the notes,' but 'Does the voice seem right?' The real question is one of vocal weight. Because it's an overlapping thing, I think I might someday do Marguerite in Gounod's 'Faust' [a soprano role]; but I doubt that I would try such dark, heavy mezzo roles as Carmen or the Verdi ladies."

The profusion of recordings by Von Stade to be released this season illustrate her special diversity: "Cendrillon", "Figaro" and "Pelleas" under Karajan; "Ahnsel and Gretel" from Cologne; Monteverdi's "Return of Ulysses" from Glyndebourne (a role she sang with the Washington Opera several years ago), and Rossini's "Otello" (a work that has been overshadowed by Verdi's later masterpiece using the same dramatic material).

In all her roles Von Stade has the reputation of being a consummate stylist. For an exemplar, she cites the late Maria Callas and describes attending one of her Juilliard master classes in the early 1970s:

"She would sing all the parts in, say, 'The Barber of Seville.' Her baritone would come just right off the page. When I got home I looked up an aria from 'The Barber and found that it is all there right in the score. You just have to learn to understand it. Quite aside from her vocal gifts, she had extraordinary musical gifts and she knew her craft precisely. And she never let the pulse of music lag. Claudio [Abbado] has this same gift. No matter how complicated things may become, the rhythm is never lost."

Another essential ingredient in her impeccable style is her scrupulous concern for language. "I do speak French and very bad Italian and worse German," she says. So until recently she has hesitated to sing in German. "I realized that in French there are certain things you must know that just don't translate. I wanted to get that facility in other languages."

She ducks the question of her perfectionist standards by noting that American singers are renowned as "hard workers" in European opera houses. "There have been people -- like Ubaldo Gardini at Covent Garden or Yuri Strasse at Glyndebourne or Mario Salerno here in Washington -- who believe that you can always go one step better, and they represent a school of music that we must be sure will continue."