Secretary of Commerce Juanita Kreps speaks so softly that it seems as if other people have been shouting all their lives in airports, on planes, in her high-ceilinged living room on the other side of the railroad tracks from her old campus office at Duke, words issue care-ful-ly and de-li-ber-ately from the spacious, flat planes of her face.

But her silences are deafening. Perfectly ladylike (as if time were of no importance) and perfectly tailored in understated variations on the theme of brown, when she's thinking something over, she drops her head into one hand and curls immaculate fingers against the bridge of her nose.

She wasted no time in establishing herself as Carter's "No woman" on the eve of her appointment on national TV, when she reminded him and everyone else that "it would be hard to defend the proposition that there are not a great many qualified women" for Cabinet posts and that "we have to do a better job of looking." Carter smiled, swallowed, and said, "I think she said she disagrees with me." She won her point, and the media praised her spirit with glee, already speculating that she might be on her way to "effective leadership."

"I really have the best of both words," Kreps says to characterize her unusual stance, poised somewhere between public niche she's carved for herself in academic, economics, business and government and her retiring domestic life in a rather glamorless, small Southern city. When asked how she manages to keep the pace with her jet-setting career and a family, too, she answers without hesitation "badly," and laughs. She has a certain liking for neatly-turned phrases.

Those who know her story dispute and modest protests of inadequacy, even mock ones. She doesn't much like to talk about her childhood in the coal-mining towns of Harlan County, Ky., except to say that her father operated a mine, that they weren't a close family - her parents were divorced when she was four, and she hasn't seen her sister in Tampa in three or four years - and that. "Everyone was having economic problems, and we weren't any worse off than anyone else." At 12, she went off to "a little Presbyterian boarding school" and then to Berea College, in Berea, Ky., a pioneer institution in work/study programs.

Her first class in economics left her knowing what field to pursue. "I was always interested in social problems, and there was massive unemployment," she says. "If you read the newspapers and had a sense of where the world was, you couldn't help being concerned. I thought economics would give me more insight into what was going on."

After graduating from Berea in 1942, she went on to graduate school at Duke, where she met and married fellow economist and Southerner Clifton H. Kreps Jr., now Wachovia professor of Banking at the University of North Carolina in nearby Chapel Hill. She juggled rearing three children with part-time teaching, and has been juggling responsibilities ever since, as professor, university administrator, author of 10 books and dozens of articles and member of half a dozen corporate boards - including J. C. Penney and the New York Stock Exchange - and numerous advisory councils and commissions.

Since her appearance on the political scene as Carter's appointee for the Commerce post, and the announcement that she would be selling her $100,000 portfolio of stocks and bonds and taking an annual pay cut of more than $35,000 to serve as Secretary (with a salary of $63,000 a year), some people have wondered how this exemplar of the Protestant work ethic came to be called Juanita.

"My mother (Larcenia Morris) liked the name, and she claimed she might have some Spanish ancestry. But with my mother, you could never be sure whether she was leveling with you or not," Kreps says. "Her maiden name was Blair, which is about as Scotchtrish as you can get. I never liked 'Juanita' - I would have preferred to be called Anne or Mary, something classic."

And so, she named her own daughters Sarah, 25, and Laura, 22, and her son Clifton III, 21. The odd thing is - deep-set eyes with Ei Greco-ish lids, a thin, arched nose, that broad expanse of brow and cheekbone.

"But I don't think I'm the Juanita type," she says. "Not fiery-tempered, not heel clicking. I should have been called Emily."

No one in his on her right mind that Kreps does look vaguely Spanish would call Juanita Kreps heel-clicking.

Her style is devastation by butt's-eye when no one expects it and everyone is looking, her remark aimed precisely without her ever having to raise her voice, and sent alone with a measure of good humor to mollify the astonished target.

People who have met her at Washington parties, where she has expressed dismayed suprise at the cattle-drive crush, have wondered whether she is "tough" enough for the job.

"When the occasion calls for it, she can be super tough," a secretary who worked in her office at Duke says.

Says Shirley Hanks, Kreps' assistant when she was dean of the Woman's College. "Juanita is a fairly demanding person to work for. She was very supportive of me and unfailingly decent to secretaries, with maybe one exception, which was a personality conflict, a matter of style. But her manner is somewhat autocratic. She never made demands, she made requests. Of course, one knew that these requests would nevertheless be filled . . ."

Some feminists may find her tastes highly suspect and her manner not autocratic enough. A former May Queen attendant while at Berea, she has been known to prefer sorority presidents to campus radicals (though she allowed her children considerable freedom) and to profess an unabashed liking for fresh flowers in her office, Sunday night supper with the whole family, expensive clothes, her own (admittedly venerable) Mercedes with her initials on the license plate and her own little rose garden (now tended, it seems, by somebody else). She also has held onto a persistent belief in being well-organized, "working within the system," making suggestions in a genteel way, and keeping her gauntlets to herself.

"I don't think you have to shy away from the idea of tokenism," she says. "It's not such a bad thing. It's just a stage we have to go through a period of 'primary education' in which we can take only small steps - one woman here, one blach there, or better, two. I don't think we should refuse to do that. The important thing is what we do after we are invited to join. To goof up on the job would be disastrous. And we have to keep suggesting - not just two women or two black men, but three or four or five or six. I am getting sort of impatient."

Author of a talk entitled, "Help! There's a Woman in the Board Room!" Kreps is invariably described by chairmen of the boards to which she once belonged as "extremely competent" and "deliberate, decisive, effective of getting her point acrsss," although none cite specific issues or policies she might have championed.

Says her collegues on te J.S. Penny board and executive director of the National Urban League, Vernon E. Jordan Jr., "Juanita Kreps was a very good and concerned director. She had great compassion for people's needs. As to specific issues, that is privileged conversation.

Kreps, who is not known as a particularly innovative economist and who generally subcribes to the theories of Paul A. Samuelson, an advocate of government participation in economic and social affairs, calls herself "an incrementalist."

"I've never felt I could just be critical," she says. "I always find it necessary to offer an alternative." She describes briefly her "alternatives" for present Social Security benefits system for women and the elderly, really "improvements," a driving for equality. "The thought may not be original but I've stated it somewhat differently and rather more often than most people," says. "And I was willing to serve on the committees and argue the case perhaps more often."

And what does the lady who says she admires the "no-nonsense, but with good grace" approach of corporate board rooms think of her first immersion in a bureaucracy?

"The whole process of appointments seems rather inefficient," she says. "In business, by the time you reach the top, you know the rules, the structure of the organization. It's a gradual, enlightened process, quite hierarchial been in government for years, one day you're a college professor and the next you're Secretary, and suddenly everybody expects you to know everything about that appointment.

A true academic, Juanita Kreps likes to do her homework; she's not one for jumping in uninformed.

Saying that she had to spend 48 hours in a hotel room before her Senate confirmation hearings, trying to absorb what she could about the structure of the department, she says,"The staff was excellent, very helpful, but as for alternatives . . ah . . there could be a longer time span between the appointment and assuming office, more overlap between the previous and the new administrations. But then, you're working with members of the opposing party, and everybody gets very uptight about that . . I probably shouldn't say too much after such a short time, but I just want to register the fact that in business, even in the media, it seems you do a better job of bringing people up through the ranks."

Determinedly unimpressed by any aura of powee which may acerue to her new position, she says, "It's my impression of people who are really top-drawer in anything that it's working harder that's made the difference."

In her first weeks at Commerce, Kreps is indeed working hard, setting the staff a precedent of "a 14- or 15- hour day," says Matt Cooney, acting director of communications. While she hasn't been eating in the cafeteria, "her lunches have consisted of sandwiches eaten at her desk," says Cooney, except for a few occasions when in honor of some visiting notable the fifth-floor executive dining room was called into service. And while ordering a review of the number of cars in the department's pool, in keeping with the administration's new austerity measures, Kreps is still being chauffeured to work in a new (as yet, unrecalled) black Mercury Monarch, maintaining that she is able to do quite a bit of reading in what would be otherwise wasted time.

"I've never met anybody who works as hard as Mom does," says Clifton III, a senior and Morehead Scholar at the University of North Carolina in Chapel Hill who is majoring in Classicw (his mother was an excellent Latin student). "I've always felt in this family that we've had a lot of independance, but certain things were expected of us - we were expected to do well in school, for example, I'd say the independance went in inverse proportion to how well you were doing."

And what of Mr. Kreps, the distinguished professor of banking? A slight, gray-haired man who drives a slightly newer Mercedes than his wife's with his initials on the license plate, he seems quietly ironic and determined to stay out of the spotlight.

"You might say he doesn't want to be in the foreground," says his son with some amusement. "I guess it's a difference of personal values. I've been really puzzling to be writing a paper now having to do with male/female relationships in ancient Greece, and I have a lot of theories, but I don't think I'd want to see any of them in a newspaper. Dad is very ironic and dry, Sometimes it's hard to tell what he's really thinking."

"He's an intellectual, fundamentally, is what he is," says Laura. She graduated from Duke last year and is studying commercial art at the Parsons School of Design in New York, where she's living with her sister Sarah, who has a graduate degree in Romance languages. "They may be apart more often now, but they've always had their own work. It's really not that different. When Mom was doing this Stock Exchange thing, she had lots to read and she would just go get Dad to explain it to her, because than was his specialty."

My father, had the sense of humor of the family," Laura says. "Whatever I have, I got from Daddy." Once in her Duke days she went about the campus with a duckling, known as "Peking Duck," perched on her pink-sweatered shoulder. "That kind of joke is really Dad's style. While Mom recognizes when things are funny, she doesn't usually make them up."

And while Clifton and Laura haven't seen much of their mother in the past month, they've had long phone conversations with her, and both say they feel closer to her - they know she's thriving.

She has found an apartment, which is "quite small and ordinary, but full of light," overlooking the Potomac, and she has a Southern girl's liking for Washington as a "pretty city," is pleased that she can look out her windows across the river toward the Washington monument. She plans to spend most of her weekends in Durham, but will hang some of Laura's paintings - whomsically abstract in white-on-white or in the light, bright colors her mother also prefers - and she's hoping her husband's teaching schedule will allow him to spend some time with her in Washington.

Kreps had spent hardly any time with Jimmy Carter in Plains, Ga., when she answered a reporter's question about "by saying she wouldn't be able to afford to live on her new salary."I said I thought I was going to have a Sugar Daddy," she says," and then someone else said, You forget that Uncle Sam is the biggest Sugar Daddy of them all" Kreps likes Carter for laughing at that.