IF JOHN F. Kennedy’s brief presidency is remembered less for its shortcomings than for its vitality, its promise, and its elevation of art and intellectual life, that legacy owes as much to the First Lady as it does to JFK himself. It was Jackie, after all, who wrote the epitaph for the Kennedy administration, invoking Camelot in a conversation with historian Theodore H. White a few months after JFK’s assassination. And it was Jackie’s personal style, combined with her youth, beauty, and linguistic skill, that enabled her to shape the course and perception of the administration at home and abroad.

The classy Chanel suits, the elegant, deceptively simple Oleg Cassini designs, the Givenchy gowns — all on display at the JFK Library — made up the stunning packaging that, even then, hinted at more. There are glimpses of that "more" in the exhibit’s huge Life-magazine photograph of Mrs. Kennedy’s tete-a-tete with Nikita Khrushchev at the height of the Cold War. One is struck by the image of Khrushchev laughing, of the humanization of this formidable foe. The accompanying text quotes an AP reporter: "The tough and often belligerent Communist leader looked like a smitten schoolboy when the ice thaws along the Volga in springtime." The viewer thaws too. It’s hard to resist a surge of patriotism, mixed with twinges of nostalgia, while viewing photographs and videoclips of Jackie’s triumphant visits to Latin America, India, and Pakistan. In these images, crowds swell the streets, cheering not only the First Lady, but American benevolence and power, its promise to reform the Third World. With our current frayed and tenuous post–Cold War relationship with India and Pakistan, we can only hope that someone with Jackie’s charisma will emerge to take up the reins of diplomacy in those lands. (Recent news stories about Lyndon Johnson’s secret tape recordings, including several with Mrs. Kennedy shortly after JFK was killed, reveal that Johnson, in what seems a brazen political move, offered Jackie ambassadorships to France and Mexico, which she turned down.)

It’s now much harder to fill the role of First Lady, to be sure. The modern feminist movement has altered our expectations of women in positions of power, yet the mantle of First Lady has changed only superficially. Four decades after Jackie graced the White House, we still hear much about inaugural-ball-gown designers, but we have yet to reach a clear consensus on how much informal power we want the First Lady to wield. Lady Bird Johnson, Pat Nixon, Betty Ford, Rosalynn Carter, and Barbara Bush — all much older than Jackie during her White House years — played the more traditional roles of hostess, figurehead, and maternal nurturer. Laura Bush, though likable and closer to Jackie’s age, also seems to fit this mold.

The wives of Presidents Reagan and Clinton stand as exceptions: Nancy Reagan, covertly, and Hillary Clinton, more directly, played co-presidential roles, and thus earned the wrath of various political factions and media. Nancy Reagan, once a Hollywood actress, never achieved the sort of icon status effortlessly commanded by Jackie. Both women’s taste ran toward the high-end, but where Jackie’s personal extravagance was matched by generous support for social programs and the arts, Mrs. Reagan paired her expensive taste with conservative social policies — which seemed to reflect a lack of compassion. And Hillary Clinton, with her succession of hairdos and schizophrenic fashion sense, seemed always to be eyeing the barometer of public opinion, like the shrewd politician she turned out to be. Clinton is also the product of a different era, schooled not in literature and the social graces, but in the decidedly less refined, arguably more aggressive discipline of law.

Yet Jackie, too, was unusually powerful by any measure. It’s well known that she touched millions of women in the early ’60s. Housewives from cities and suburbs across the nation imitated her hairstyles and clothes. But her appeal went far beyond that. We now understand that she possessed keen intelligence and a complex inner life that compelled her to transcend the limits imposed on her. Like Eleanor Roosevelt, Jackie struggled to find ways to contribute her voice to the world within the framework of women’s role. As the exhibit makes clear, Jackie expressed herself, not in policy or print, but in her choice of dinner guests and designers. We don’t know what this channeling of her talents might have cost her — spiritually and emotionally — or whether the nation gained more or less from her as a result. But we do know that she modernized the White House, and did so with dignity and exquisite taste, turning it into a place where men of power mingled with poets, where Pablo Casals played the cello, where actor Basil Rathbone, at Jackie’s insistence and direction, recited Shakespeare and Marlowe.

FOR ALL that, however, Jackie endures as an icon as a result of several self-reinventions undertaken in the years after she left the White House. Right from the start, she asserted her autonomy and independence from the powerful Kennedy family. She avoided the press; she even risked a public-image disaster by marrying Aristotle Onassis in 1968, just months after Robert F. Kennedy’s assassination. But years later, when Jackie whisked her children off to a Greek island and out of harm’s way, the public viewed her decision favorably, as the protective act of a loving single parent. Her parenting skills would later be applauded, as the adult Caroline and John Jr. handled the spotlight not like spoiled scions of fortune, but like their mother — with simple grace.

After Onassis died, when Jackie was in midlife, she again reinvented herself, this time as the editor she might have become had she not married into a political dynasty. She edited books, first for Viking and then for Doubleday. She also threw herself into efforts to preserve architectural landmarks in New York City, most notably Grand Central Station.

For her insistence on becoming mistress of her own destiny, Jackie earned the respect of a number of feminists. Take, for example, Gloria Steinem’s 1979 essay "Jackie Reconsidered": "Her example poses interesting questions for each of us to ask ourselves: given the options of using Kennedy power or living the international lifestyle of Onassis, how many of us would have chosen to return to our own talents and less spectacular careers? How many of us would have the strength to choose work over derived influence? In the long run, her insistence on work that is her own may be more helpful to other women than any use of the conventional power she has declined."

But Jackie’s single-minded assertion of independent judgment was evident during her White House years too. One of the more revealing parts of the exhibit — easily missed amid the clothes and commanding photographs — is a typewritten page of 20 questions submitted to the First Lady by UPI reporter Helen Thomas. Jackie’s handwritten answers are in the margins — pitched in the same way, one guesses, she might have jotted notes to an author in later years. Thomas asks if Jackie thinks there is undue interest in Caroline and JFK Jr. "Yes," is the straightforward reply. Then a follow-up question about the children: does living in the White House add to their lives and sense of history?

"They are too young to have a sense of history," writes Mrs. Kennedy. "That we have managed to keep them close to us in the White House I hope will add to their lives."

Finally, Thomas asks Mrs. Kennedy if she plans to write a book about her White House years. In block letters, Jackie etches a simple "NO."

The exhibit includes only a brief mention of JFK’s assassination, yet its specter hovers over everything, providing a somber subtext to the exhibit’s glamorous images much as September 11 is never far from consciousness as one stands there gazing on all the dresses and photographs. Past and present, promise and poignancy, blur in one unlikely image that appears at the show’s end: a video clip of the youthful First Lady, casually elegant in a headscarf billowing in the wind, cradling her toddler son, John Jr., in her arms. In that image of youth and hope, it is achingly impossible not to reflect on what the future would hold for both of them. For all of us. In the next moment, the door leads from the exhibit into the bright main hall, with its stunning view of Boston Harbor and the city skyline. The past suddenly pulls up to the present, as earth and sea meet sky, and mourning gently gives way to gratitude.

Loren King can be reached at Lking@86958@aol.com