What makes Jacqueline Onassis the most famous woman in the world, or, as the writer Stephen Birmingham would have it, "the most famous woman in history since Cleopatra?" Why is it that her name, her photograph, sell more newspapers and magazines than Princess Margaret's did? Other celebrated woman make news from time to time, but none has ever matched Jackie in holding the continuous, ravenous interest of the public, year in and year out.

She is 50 years old today. How long can she continue to cast her spell? How did it start and why has it lasted? How much of it is due to historical chance, how much to her own manipulation of her image, how much to the public's obsessive appetite for just plain phony baloney?

She's no great beauty, although it must be admitted that compared with preceding first ladies of the United States, such as Mamie Eisenhower and Bess Truman, she was sensational. She was young and photogenic, but in person her looks were, and still are, inferior to those of almost any model, most film stars, many socialites, even girls you pass on a street or see in a store or restaurant. Her legs are not particularly good, her hands and feet are too big (she wears a size 10 shoe), and her figure is flatchested and ordinary. Those notorious nude pictures taken by telephoto lens when she was sunbathing on the Greek island of Skorpios would never have caused a ripple of interest in any editor or reader had she not been who she was.

So, it's not just her looks. It's not her clothes, despite her insatiable extravagance, because thousands of other women have more style. It's not her fortune, now estimated at somewhere between $30 and $40 million, because there have been, and are, far richer women. The late Barbara Hutton, was one, and Doris Duke of the American Tobacco fortune still is. So too is Christina Onassis, but despite the interest in her curious marriage, no one particularly wants to see her nude.

It is certainly not as a sex goddess that she holds the world enthralled. People who have known her describe her as neither seductive nor sensual. In fact, they waste a lot of time wondering if she is intimate with this one or that one of her many escorts - or with none. There is something standoffish about her, inaccessible, aloof. Although she had had affairs before she married Jack Kennedy, she couldn't possibly have had a satisfactory sex life. Bad back or not, he was the most sexually active president the United States has ever had but not, it seems with his wife. Jackie new about it all, or, if not all - her husband had hundreds of other women from secretaries and hotel maids to starlets, socialites and wives of his friends - she knew the score. She chose to ignore the shenanigans and go her cool, regal way.

After all, it could never have been called a love match on either side.

Jack was a young senator and it was no secret that his father, Joe Kennedy, then worth about $400 million, was determined to make Jack president. He pushed his son into the marriage because Jacqueline Bouvier's social position was superior to the Kennedy's. She had been to the right schools, had an inpeccable reputation, and was a Catholic - all important assets for JFK's political future. As for Jack, he was never in love with her. During their courtship, while he was having an affair with her, he was also sleeping with other women. It was a marriage with calculated benefits for both bride and groom.

Some Jackie-watchers have concluded that it was the aura of the Kennedy charisma that first captivated the public. Jack had it and Bobby had it and Ted has it. But people don't trample each other to get a glimpse of Ethel or unhappy, beautiful Joan, or any of the rollicking Kennedy sisters. It was Jackie herself who stimulated the intense public interest in every move she made. Although hers could not have been a joyous marriage, she appreciated her prestige as first lady and was acutely conscious of her role in history. She was furious when she learned that her trivial notes to servants about household matters were thrown away. She demanded that every scrap of paper from her to be preserved for posterity. (Probably correctly so. Think how interested people would be in Martha Washington's notes to her cook.) She redecorated the White House, giving it charm and elegance. Although she had art gallery directors, history experts and professional decorators to do the actual job, at least it was her idea and she was the overseer. When she appeared on television to show off the results, Norman Mailer wrote, "She walked through it like a starlet who is utterly without talent."

Every detail of what she did was eagerly devoured by the public, and the worse she treated the press the more the public's appetite was shetted. She refused all interviews; she forbade her staff to reveal what she ate, wore, read or said. Inevitably this had the effect of creating a whole new industry: gatherine Jackie items by hook or by crook. There have been some 25 books written about her in English, most recently Kitty Kelley's bestselling and informative "Jackie Oh!" There are bound to be more.

There was plenty of material to be ferreted out. Her refusal to attend functions ordinarily an integral part of a first lady's routine and her stubborn flouting of official duties left the nation pop-eyed but fascinated. Right from the start, she was obviously a different breed from the usual political helpmate. On Inauguration Day she refused to attend a reception in honor of Vice President Lyndon Johnson and his wife and she ignored parties given to honor those who had run the election campaign.

During her reign Jackie refused to visit hospitals, no matter what the cause or occasion; she never appeared at Democratic fund-raising parties; she declined to attend a luncheon of the National Council of Negro Women and went fox hunting instead. When the wives of congressmen and senators gave their traditional lunch in honor of the first lady (they had collected money to buy Jackie a $150 bottle of French perfume and other gifts), she put her foot down and wouldn't go. The president went in her place, rather than insult the congressional wives, whom Jackie described as silly and boring.

The country was treated to the intriguing spectacle of a first lady who spent four days a week at her fox hunting retreat in Virginia, traveled without her husband to Italy where she was photographed with her frequent escort Gianni Agnelli, head of the Fiat empire, and who spent more than $105,000 on herself in her first year at the White House. Regular White House expenses were paid from taxpayer's money, but Jackie's personal bills, mostly for clothes, were sent to Joe Kennedy's office to be paid.

That Day in Dallas

When she traveled without her husband to Europe or Asia, she was received like royalty, although the visits were unofficial. (JFK encouraged these trips, possibly to leave the White House free for his girlie sprees.) The trips added lustre to her fame; wherever she went vast, enthusiastic crowds cheered her.

Then came the dreadful day in Dallas, which left her not just a celebrity but a tragic heroine, a magical symbol. Her poise, her strength, her dramatic sense of history stunned people in all countries. She refused to change her bloodstained pink suit, she didn't sleep, she never wept. Television cameras from around the world recorded for all time her extraordinary stamina and dignity.

Arriving back at the White House on that night, she arose at 4 o'clock the next morning and began to plan every detail of the funeral, determined to model it as closely as possible on that of Abraham Lincoln. She overruled the Kennedy family on the choice of a church; she herself walked behind the cortege the eight blocks from the White House to the church and she chose the Black Watch pipers to accompany the bier. Every detail was planned with an eye to the greatest theatrical effect. She chose Arlington National Cemetery - his family wanted the family plot in Massachusetts - and the eternal flame was her idea. She lit it herself on the burial day, and there was scarcely a dry eye throughout the world among the millions who watched the scene on television. Not once did she break down, although one photograph shows an expression of grief.

At the White House reception she actually looked radiant as she greeted the dignitaries, smiling and shaking hands with Prince Philip of Britain, Emperor Haile Selassie, President de Gaulle and other heads of state. Later, she went upstairs to the family sitting room to participate in John Jr.'s third birthday party, which she had refused to postpone. It was an unprecedented performance and left her unquestionably the most admired woman on earth.

After an Adriatic cruise Jackie assumed her new role as America's widowed queen. She was the first widow of an American president to have Secret Service protection for herself and her children, as well as an office and a secretarial staff, all at taxpayers' expense. No one begrudged her this, even though she refused to attend any functions, not even the dedication of the Jacqueline Bouvier Kennedy Rose Garden at the White House. She moved to a luxurious Fifth Avenue apartment in New York and busied herself with plans for the John F. Kennedy Memorial Library. She seemed paranoiac about the press who now, of course, pursued her even more intently.

After a reasonable length of time, she began to be seen with various escorts such as Mike Nichols the director, Charles Addams the cartoonist, Frank Sinatra and, above all, Lord Harlech. Harlech was a widower and old friend, and it was expected that they would marry. They traveled together, visiting Cambodia and other places. Despite all the speculation, it is possible that their relationship was platonic. If she had married him, she would have become Lady Harlech, another American hostess in London or Wales, married to a British title. Eventually the fuss and furor would have diminished and then ceased. She was not ready to relinquish her imperial role.Anyway, he may never have asked her.

When a stunned world learned that she was going to marry Aristotle Onassis, the horrified reaction was, "Why? What on earth does she see in him?"

Contrary to popular myth, he was not a rags-to-riches, rough-hewn, slum product. Born in Smyrna where his father was one of the richest tobacco merchants in the region, his family was upper class. He received an excellent education and was set to go to Oxford when Kemal Ataturk moved in on the Smyrna Greeks. Onassis' three uncles were hanged for political reasons. For Onassis' safety, his family decided to send him to Argentina. He was only 16. He traveled on a Nansen passport for stateless refugees (named after the Norwegian explorer who was awarded the Nobel Peace Prize). In Buenos Aires he got a job as night telephone operator, learned Spanish by listening in and when through work at 7 a.m., sold tobacco samples from Greece. "Sleep?" he said to me, laughing. "Who needs sleep?"

By 1930, he had made enough money to buy six secondhand Canadian freighters in Montreal. He made his first million the year he was 25. He never stopped. "It is not a question of money any more," he told me. "After you reach a certain point, money becomes unimportant. What matters is success. I know that the sensible thing would be for me to stop now. But i can't do it. I have to keep on. Not for the money, but for the thrill. I must keep aiming higher and higher" - he paused and shrugged his shoulders- "even though I know how silly it is."

Marriage to Onassis

There was a constant farcical rivalry between Onassis and another shipping magnate, Stavros Niarchos. Onassis had married Athina Livanos, the beautiful, 16-year-old daughter of Stavros Livanos, yet another Greek tycoon. Niarchos divorced his first wife and married Athina's sister Eugenie. From then on, the rivalry increased. The two men played tick-tack-toe with tankers. Every time Onassis built a big one, Narchos built a bigger one, only to be topped by Onassis again. And so it went. Onassis bought an El Greco. Niarchos bought an El Greco. Onassis bought the Christina, a 322-foot Canadian destroyer-escort and had it rebuilt inot the most luxurious yacht in the world. Niarchos bought the Creole, the largest privately owned sailing ship. When Onassis entertained Winston Churchill, Greta Garbo and other hoity-toity celebrities on cruise-. Niarchos hired Elza Maxwell, a dreadful woman who made a living by introducing people to each other, and she rustled up a clutch of movie actresses and Aly Khan for a cruise on the Creole.

And what was Onassis' final, devastating coup? Divorced from his wife becuase of his long affair with Maria Callas, he married the most famous woman in the world, Jacqueline Kennedy. "The only way Niarchos can top that," I said at the time, "is if he runs off with the queen of England."

There was no suggestion of his being in love with her. He acquired her as he would have acquired a renowned painting, say a Rembrandt, generally considered unobtainable. She was the final feather in his cap, the ultimate stroke to startle this world and further enhance his prestige. Nor was there any question of her being in love with him. Her primary interest was and is herself. She is a woman who probably has never loved any man except possibly her dashing, snobbish, drunken father, "Black Jack" Bouvier. What she saw in Onassis was escape from the Kennedy clan, absolute power and protection and, above all, unlimited money. Despite her $10 million inheritance from Jack Kennedy, no amount of money would ever be enough for her, as Onassis was to learn.

Meanwhile, she was mistress of Skorplios with 72 servants at her beck and call. She had at her disposal another Greek villa with 10 servants, a hacienda in Uruguay with 38 servants, and a Paris penthouse with five servants. Onassis gave her for herself a Fifth Avenue apartment in New York with five servants and furnishings that included paintings by Van Gogh, Picasso and El Greco, although when he himself was in New York he stayed more often than not at the Hotel Pierre.

A Life Apart

To the mystification of the public, they more or less went their own ways.Reports of his fabulous gifts were eagerly lapped up: a ring with a ruby the size of an egg, surrounded by dozens of one-carat diamonds, with matching earrings; a 40-carat diamond ring for her 40th birthday; a $60,000 sable coat; a diamond necklace, earrings and bracelet worth $1 million. He spent $20 million on her during their first year of marriage, in addition to his prewedding present of $3 million in tax-free bonds. Her clothing bills were astronomical, despite her monthly allowance of $43,000. Nothing seemed enough. Creon Brown, his financial manager (who had arranged my interview with Onassis 12 years earlier), began getting telephone calls from her secretary, asking for more money.

Before the wedding, Jackie went to see Archbishop Cushing of Boston, the Kennedy family prelate who had married Jack and Jackie. Afterward, the archbishop spoke on television. He said that the coming marriage was not what it was generally supposed to be and that if people only knew the truth about it, they would understand. "But my lips are sealed," he ended. Then it struck me. Of course. The Catholic church recognizes first marriages as binding until death. Onassis' first wife, Tina, was still alive. Therefore, in an ordinary marriage, Onassis and Jackie would be considered as living in sin. However, if the couple lived together without consummating the marriage, Jackie could continue to receive the sacraments, as indeed she did.

Onassis was dynamically male. Jackie was his wife. He may have insisted on exercising his conjugal rights. On the other hand, he may have stuck to his part of the bargain. She was definitely not his type of woman. Maria Cellas was, and he continued to see her. It was obvious that a man of his intellect and wide interests would become bored with Jackie's shallow life, her wild extravagance, her pretentiousness.

Their quarrels became more frequent, even in public. He consulted the lawyer Roy Cohn about divorcing her. Through his influence with the Greek junta then in power, he had a law passed to provide that, after the death of a Greek citizen married to a foreigner, the foreigner would have no claim on the citizen's estate, contract or no contract. He made a new will, leaving her $200,000 a year for life, plus $25,000 a year for each child until the age of 21. The bulk of his fortune went to his daughter Christina.

He became increasingly ill and died in 1975, while Jackie was away in New York. She flew to Skorpios for the funeral and was cold-shouldered by his family, who had always resented her. She refused to accept his changed will and pushed for more, declaring that she would accept no less than $20 million. Finally, to get rid of her, Christina settled $26 million on her and Jackie renounced further claims.

Onassis was the only man she could have married and still retained her role as America's queen and the most famous woman in the world. He was the best possible match, the only possible one, from that point of view.

What does she do now, at the age of 50? She still has an exalted idea of her own superiority, thinking of herself as the equivalent of royalty, which, to Americans, she appears to be. Our infatuation with someone like her derives from North America's heterogeneous population of immigrants. We have an innate hunger for aristocracy, although what is considered to be the aristocracy of the United States today started out, with some exceptions as immigrant fur traders, gold and silver miners, oil prospectors, peddlers and, in many cases, identured servants and deported criminals. The leaders of the early settler groups may have come from the upper classes of Europe, but their followers, the rank and file, were definitely not patrician. From log cabin to White House, from office boy to company president is the American way. Jacqueline bouvier, has been like a princess - imperious, extravant, remote from the common people. But she had been notably lacking in one quality of bona fide royalty. That quality is noblesse oblige, which the dictionary defines as "the obligation of honorable, generous and responsible behavior associated with high rank or birth."

True aristocrats feel it is their duty to be gracious to those of humbler rank. Jackie is frankly a snob and has never bothered to disguise it. Nor did she feel it necessary to fulfill the customary rites of a first lady, no matter how boring she found them, or to show an interest in the social welfare of her people. She has not changed. True she has recently worked in a couple of publishing houses, but her contributions have been less than spectacular and her performance as a "working woman" has resembled that of Marie Antoinette playing at milk-maid in the Petit Trianon. CAPTION: Picture, no caption, UPI