Nancy Thurmond has been an enigma ever since she came to town as the beautiful bride of Republican Sen. Strom Thurmond, crusty South Carolina legend. Many wondered why a 22-year-old former beauty queen would marry a 66-year-old senatorial institution. Now, 13 years and four children later, people are wondering why Nancy Thurmond has rushed on social Washington this season like a southern gale.

"I don't take on frivolous, superficial projects," she says. "It's not a scintillating, gossipy atmosphere on my part. When I take on a project outside the home, it's usually something involving children, or something that I perceive as helping Strom in my own way. That's one of the reasons we have maybe had a staying power in Washington."

In September, she gave a tea for 600 women in honor of Supreme Court Justice Sandra Day O'Connor. U.S. Ambassador to the United Nations Jeane Kirkpatrick, establishment Democrats, even Barbara Walters came. Nancy Thurmond was pert and poised at the head of the receiving line, which made four bends through the dark corridors of the Russell Building. "Nancy, in her usual, thoughtful way," said Peatsy Hollings, wife of Sen. Ernest Hollings (D-S.C.), "has invited all of Washington."

In October, she had an eight-course dinner at the expensive Le Pavillon restaurant for the 30th wedding anniversary of Leonore Annenberg, outgoing U.S. protocol chief, and Walter Annenberg, former U.S. ambassador to Great Britain. It was clubby and cozy. Strom Thurmond marveled that Walter Annenberg, 71, was able to keep up with his wife, 61. "Nancy has the same problem keeping up with me," he said. "And I wanted to give you a small gift which hopefully will help you in the next 30 years to keep pace with your active wife." It was a package of stress formula vitamins.

In December, Nancy Thurmond appeared for a party at the Moroccan Embassy, a striking presence of black velvet, gold braid and aplomb. Unlike most political wives who make the Washington nighttime rounds as afterthoughts, Nancy Thurmond arrived like a star. The cameras clicked, the hosts kissed. On her head was a closefitting fur cap that she wore through the evening, a dramatic -- if unusual -- cover for her blondish-brown curls. There was no way to miss her.

Nancy Thurmond has her own public relations consultant to handle the large-scale entertaining. Mary Pettus of Mary Pettus and Associates Inc. arranged Nancy Thurmond's tea for Justice O'Connor, the dinner for the Annenbergs (part of which was paid for by Le Pavillon as a promotion), a dinner for 24 for Justice O'Connor at the Shezan restaurant, a benefit for the Washington Chamber Orchestra and a coffee for society columnists Betty Beale and Ymelda Dixon. Pettus, who is a friend, is unpaid by Thurmond except for thank-you notes and the contacts she acknowledges she makes through Nancy.

"A lot of her activities are misinterpreted," Pettus says.

Pettus, an ambitious professional who is paid by her corporate and restaurant clients, helps prepare the bulk of Thurmond's guest lists. She also arranges for food, decides on decorations and, in the case of the coffee, she hand-embroidered two Christmas tree ornaments that were likenesses of Beale and Dixon. They received them as presents.

So what is Nancy Thurmond up to?

There are several schools of thought:

* Some, particularly political liberals, think that underneath the sweet, southern exterior is an icy calculator, a modern-day Scarlett O'Hara who wants the Senate seat of the husband some say she married for power. "They've built a lifetime out of being political animals," says the wife of a South Carolina Democratic politician. "She understands the tremendous machinery that they have, and she couldn't possibly let it lie fallow."

"But I don't see how all this is going to help her in South Carolina," counters Peatsy Hollings. "Her husband is not going to live forever, so I think she has decided she had better try to find a niche for herself. She's probably looking to find some kind of media thing."

(Strom Thurmond's Senate seat is up in 1984. At 79, after almost three decades in the Senate, he says this is his last term. But then he adds: "A lot of people are asking me to run again, so I'll have to consider that.")

* Others, including her friends, agree with Nancy Thurmond when she says of herself that "what you see is what you get . . . but it's not peaches and cream and hunky-dory." "Yes, she really is sincere," says her friend Mary Jo Campbell. "She really does care if you have strep throat, if your husband lost his job or if your house burned down." Many say she's merely performing her extensive duties as wife of Strom, the new chairman of the Judiciary Committee and president pro tempore of the Senate. They also say she has more time these days because her children are older.

And one friend, asking for anonymity, reasons: "With her husband as president pro tem of the Senate, there are so many opportunities to take advantage of. She's like a kid in a candy store."

* A third group doesn't know what to make of her, although it watches intently. "I really am fascinated by her," says Carrie Lee Nelson, wife of former Wisconsin senator Gaylord Nelson. "That mind must be going a mile a minute. She's touching all the bases at all times, she never gets impatient, never seems irritated. Now, what she does in that little dark corner of her house -- I just don't know."

And there is always the enduring, tantalizing appeal of the Strom and Nancy show that for all its doomsayers, appears alive and well in McLean. "Hell, I don't understand it," says Gay Suber, the South Carolina pol who's known Strom Thurmond for 34 years.

But still there are four children, moments of handholding, a canopied, four-poster bed -- and a sense of survival through what Nancy Thurmond calls "an era when divorce was easy to come by."

They have their own brand of humor. Nancy Thurmond sometimes scans the birth announcements, telling her husband she's just found his next wife. "We've had a wonderful, wonderful marriage," she says, "although it's not been easy -- it's been hard. It ends up being 99 percent give if you're going to make it work."

("Strom is, as most husbands are, demanding," says Campbell. "He loves Nancy to do things right away. If the children want a dog, he'll say, 'Nancy, go out and get a dog' -- not realizing that the same week she has to be in South Carolina and up on Capitol Hill. He keeps her hopping.")

For the record, Thurmond says she has no interest in political office. "We were very, very active before," she says, "but I guess by virtue of the fact that we were in the minority, we were less visible. It's basically the same involvement we've always had."

This means nothing to the Washington watcher, especially when Strom Thurmond says: "I've encouraged her, at some point in her life, to get interested in politics . . . she'd make an ideal public servant -- senator, governor, whatever."

"He has never told me this," says Nancy Thurmond, appearing startled. "I mean, this is something new." Art From Politics

In 1974, a newspaper article described Nancy Thurmond as "slightly matronly . . . filling out around the waist with just the slightest hint of a double chin." Today she is slimmer, dressing carefully in pretty, flattering suits and ruffled blouses. She has a beautiful, doll-like face, big eyes, a full mouth and perfect teeth.

In an interview she can be relentlessly formal. Her answers are weighed and measured, then dispensed with a large dose of sunshine. She is wary of reporters, not least because she is often described as cotton candy. She isn't, although it takes her time to remove the armor of poised political wife. One way is to tell her that some people think her charm and good works are fronts for a schemer.

"I have never considered myself calculating at all," she says, the smile and sweetness gone. "And I have never self-analyzed myself at all. What I find disheartening is that, in your sphere, good intentions have to be attributed to an ulterior personal motive. I am what I am."

Spending a day with her is running from luncheon to charity meeting to cupcake-making to schoolyard to gymnastics car pool to Capitol Hill to art opening to dinner dance. It's not unusual for Nancy Thurmond to get up at 2 a.m. to answer mail until 5:30 a.m., when she'll jog around her McLean neighborhood with her husband. Then the family has breakfast together.

"I haven't slept-in in 10 years," she says.

"The things that are the stuff of human life," says a former South Carolina political opponent, "like going to a movie and crying, or a father sitting in a room reading the newspaper, doing nothing, not making political phone calls, not doing push-ups . . . I wonder if that doing nothing is part of their lives.

"I think the forms of political practice are brought to a high art by the Thurmonds. By that I mean the letter that goes out of the senator's office to every graduating senior in South Carolina. Every senior, every year. The ultimate was this: I had two or three friends tell me that on Christmas Eve, about 8 o'clock, they got a call from Nancy Thurmond. 'Strom and I were sitting here by the fire and we were thinking about you.' Their lives are politics. Christmas Eve is a time to politic. And I'm telling you, it's worth some kind of gold -- Strom Thurmond was thinking about me on Christmas Eve? It's unbelievable."

A recent day of Nancy Thurmond's has less to do with politics than with the threads of a tightly woven suburban life. She attends a lunch and private fashion show at the Watergate apartment of designer Frankie Welch, then goes with Trish Lott, wife of Rep. Trent Lott (R-Miss.) to Ford's Theatre for a charity meeting. There they meet with the theater's executive producer, Frankie Hewitt, Mary Pettus and people from the Washington Chamber Orchestra. The subject is the benefit for the orchestra at the theater. Thurmond is honorary chairman; Lott is co-chairman.

Thurmond takes a seat, then addresses the group. "I'm so glad you decided to utilize your own talents," she says. "I think that's wonderful. I have not been involved in chamber music in Washington, but I would like to tell you that my roommate at Duke was an oboe player." She leans forward in her chair, ankles neatly together, then looks intently at a man from the orchestra. "You have done some composing yourself, haven't you?" she asks. A few moments later, she turns toward Hewitt. "I just mentioned to Trish that the last time I was here was for your gala," she says. "What a lovely evening, and how successful that was. I think you're kind of the key to the success."

"She has an elephantine memory," says Charles "Pug" Ravenel, who lost to Strom Thurmond in the 1978 Senate election. "She's excellent at the peripherally important but vital parts of the political process -- how you deal with people, remembering their names and so forth."

"A consummate politician," says Rep. Carroll Campbell (R-S.C.), who's known her for 14 years.

From the theater meeting, Nancy Thurmond heads toward McLean because the kids -- Nancy Moore, 10, Strom Jr., 9, Julie, 7, and Paul, 5 -- will soon be finished with school. Friends say Nancy Thurmond is an involved, organized and rigorous mother. Certainly, her conversation is evidence; during the course of this particular day, she talks about Nancy Moore's homework, Strom Jr.'s birthday party and Julie's knack for gymnastics. "You're so busy looking after the needs of others that you cease to think of yourself," she says. "We've been swept up in a me-ism cult. But because there are so many people saying 'Mommy' and 'Nancy,' I just don't have time to think about myself."

Doesn't that bother her? "It's the way it is," she shrugs. Mother's Day

The house is a picture-perfect two-story colonial at the end of a cul-de-sac, complete with an American flag and an old tire swing out front. The living room is done in light blue wall-to-wall carpeting, light blue walls and red Victorian chairs. The family room is a mishmash of wooden benches, comfortable red leather chairs, a map of South Carolina and a picture of Strom, wearing a light blue tuxedo and a butterfly-like bow tie, as he meets British Prime Minister Margaret Thatcher.

The bedroom is done in rust, with shades drawn. There is a small set of wooden steps leading up to the large bed. "Oh, that's for the kids," says Thurmond. "You know, 'cause they're always climbing into bed with us."

In the kitchen are knick-knacks, a housekeeper and homey sayings. "Recipe for Happiness," says one wall hanging. "One full measure of kindness, a dash of laughter . . ." "Tommorrow begins today," says another.

Thurmond makes cupcakes because Strom Jr.'s birthday is coming up and he has to bring something for his class. She ties on an apron, spilling not a drop of the batter on her suit.

("Did you see last year's 'Moment With Nancy' on Deena Clark?" asks Peatsy Hollings on a later day. "I can't remember what was so hysterical, but the children were making Christmas cookies and even that was organized. You would have thought there would have been flour flying. But no.")

Thurmond puts the cupcakes in the oven, then leaves for school to pick up Nancy Moore and Julie for gymnastics practice. Today is her car-pool day, which means inhabiting a station wagon for half an hour with seven squealing girls. As is the custom, Nancy Thurmond has brought along doughnuts and Hawaiian punch for the girls to eat on the way to practice.

"Nancy Moore," she says to her daughter as she drives, "now listen to me, honey. You need to get your hair clipped back before you get to gymnastics. You brush your hair, and then you can have your snack."

Nancy Moore does this in the back seat, then pours the punch for the girls. "OH NO!" they squeal as the car hits a bump.

"Drink it fast!" says Nancy Thurmond, "before we hit the bumps!"

"HERE COMES ANOTHER BUMP," say the girls. "AAAAAHHHHHH!"

After this crisis, Nancy Moore tells of another. "Rachel is such a pest," she says to her mother. "She went up to Eric and said, 'Do you like Nancy?' and he said, 'Yessssssss.' And then Rachel came out and said, 'Hey, you guys, Eric likes Nancy!' "

The girls scream.

"Now you all have to be little ladies," says Nancy Thurmond. She leans her head on the car window, putting a hand on her brow. She smiles just a little. Model Child

Nancy Thurmond watchers will tell you that she was raised by a stage mother who set off her ambition. "My friends don't say that," counters her mother, Julie Moore, an attractive woman with a bouffant of dark hair. "We wanted her to do what she wanted."

Nancy Thurmond grew up in Aiken, S.C., a middle-class girl in a rich resort town known for its horsey crowd and Rolls-Royces. Her father worked at the nearby Savannah River Atomic Energy Plant. Her older sister is a psychiatrist in San Francisco. Her older brother is in the aeronautics business in New Hampshire. Neither wanted to be interviewed about growing up with Nancy.

"She was the easiest of the three," says her mother. "Any time she misbehaved, we'd find a note under our pillow saying she was sorry . . . she didn't go through that awkward growing-up age, at 11 or 12. She always seemed to grow up pretty -- never too gangly, or too plump. And she never had to wear braces."

Julie Moore says it was Nancy who wanted to be in the church choir, the youth group, the French club and the local beauty pageants. "She's been a hard worker all her life," she says.

"The mother was the power behind Nancy," says John Akins, her 10th-grade English teacher. "Her grades would alternate from A to C. She'd make A's in grammar, punctuation, spelling -- and then when we got to literature, she wouldn't be interested and she'd make a C. Her mother did go to the principal.

"A lot of change probably occurred between her junior and senior year. At first she was pretty honest -- she said what she thought. You know, 'I like that, I don't like that.' She would get under my skin occasionally, and that was fine. Then she started slowly covering up, and didn't blurt out what she was thinking. It was a learned process. By the time she was a senior, it was, 'Oh, isn't that nice.' All of us learn that, to do things that help us get along in society. But she's such a super-smoothie."

Nancy Thurmond went on to Duke University, took a leave to spend a year touring the state as Miss South Carolina 1965, then returned to finish. "Her every step was planned," recalls a close friend from Duke who asked that her name not be used. "She used her Miss South Carolina office as an entree to political people, not an entree to performing . . . she didn't have a lot of close friends, but the student body thought well of her. I think her social life with men was . . ." She hesitates. ". . . only average. She didn't go out as much as you would have thought a beautiful girl would go out. She had trouble not wanting everyone to like her because she was a beauty queen. It was a wishing -- 'I wish I could find some man where I could be myself. I don't think she had much of the feeling of 'I'm having a really great time.' "

It was during this period that she was getting to know Strom Thurmond, the South Carolina institution and one-time leading segregationist. Famous for his highly successful door-to-door, church-social politicking, Strom Thurmond, opponents have said, could strike up a conversation with a doorknob.

He had first called Nancy from Washington to congratulate her as Miss South Carolina, and they'd met soon after that at a Grape Festival in York, S.C. Strom asked Nancy to join him and several other couples for a square dance in nearby Clover. "We just hit it off," Nancy Thurmond recalled in a 1974 interview. "He and I just had this rapport, I guess you could say. And that was unusual, not only because of the age difference, but because I was not at all involved in his big world. But with his wit and my conversation, well, it just kind of worked."

At school, Nancy Thurmond found herself looking forward to his calls. "I would go out on a date and when I got back to the dormitory," she said in the 1974 interview, "sometimes Strom would call me just to talk. It got so that I would think about his phone call during my dates and I would be so anxious to get back so I could talk to him."

Strom proposed the summer before she entered the University of South Carolina Law School. She thought about it for three months. Then she dropped out of law school and, after arguing about the age difference with her parents and his political aides, married him. Stands by Her Man

The senator's office is lined with plaques, citations, awards, autographed pictures of presidents, flags, souvenirs. On a mantel are pictures of the four children. Nancy is here, changed into black silky culottes for her evening activities.

"That mantelpiece shows some of her activities," says Strom. He is in a hard, straight-backed chair with his legs apart, feet planted firmly on the floor; Nancy sits just to his left, her legs crossed. An elbow rests on one knee.

"She's very smart, she speaks well, she writes well," says the senator. "She knows more people in the city of Washington, and does more good than anybody else. Her talents are so valuable that I think she should be freed for the good of the community."

"He's a real feminist, isn't he?" she says, genuinely pleased.

"I just don't think we're capable of seeing what they see in each other," says Gay Suber, the former executive director of the South Carolina Republican Party who's known Strom Thurmond for 34 years. "But it's sincere. What they have, however it got there or why it got there, whatever it is -- it's there. I've seen the affection he has for her, and it's not just physical, it's beyond that.

"I know of conversations that took place when they were discussing getting married -- I know of some of the intimate, intimate details of the conversations, and I'll tell you, a friend of mine who was a friend of theirs was talking to them, and he was brutal, absolutely brutal. He sat down there and said things that other people thought -- 'How can you do that with him?' Well, the reaction of both of them was not anger. They said, 'We're sorry, but neither of us has ever done things in life because of a consensus.'

"I was convinced later, sitting around talking with them, that there was nothing fakey about it. I can't be fooled that well. I used to be nice to her because she was his wife, but I just didn't have any respect for her. But now, because of the time I've spent with them, I know better."

The visit with Strom is up. He stands, claps his hands, then kisses her softly on one cheek. She leaves with Holly Johnston, all-purpose aide, in a Ford Grenada with "U.S. Senate 1" South Carolina license plates. Nancy Thurmond sits in the front, then pulls down the sun visor to check her lipstick in its mirror.

"You know, nothing catastrophic occurred today," she says, carefully outlining her lips. "The main thing I've got to do tonight is get those cupcakes packed up."

The car moves on in the dusk, toward her evening activities. Two more parties, and she'll be home.