THERE IS ALWAYS DRAMA, if not always poignancy, in a story of the mighty fallen. But while presidents, military dictators and the like have their following, it is royalty that draws the biggest crowds. They will not be disappointed in the first royal memoir of the Pahlavis of Iran since the revolution.

Living in exile in New York and inactive for the first time in her turbulent life, Princess Ashraf, the twin sister of the shah, has had time to ponder the past and watch the international crisis that followed the revolution.

Princess Ashraf's memoirs are frank, well-written and devoid of self-pity, though they are not as revealing as the publisher's blurb would have us believe. Her story runs as two levels, the personal and the political, with comments and judgments on international diplomacy woven into the fabric as she goes along.

From it emerges a courageous, independent-minded woman who, whatever you think of her privileged position and her politics, rarely chose the confortable option and often deliberately swam against the tide. But even for those who are fascinated by royalty, the question must arise at the end of it all: If that is what you have to go through, who would want to be a princess?

Princess Ashraf's personal misfortunes would provide enough plot material for half-a-dozen romantic novels. Her childhood was lonely and unhappy, overshadowed by her twin brother -- the heir to the recently created Pahlavi dynasty -- and her elder sister, her father's favorite. There is a telling picture in the book showing these two on their autocratic father's knee and little Ashraf standing forlornly at one side. Her much-loved brother was killed in a plane crash. She was forced into a miserable first marriage, endured a respectable but unloving second union and only found marital satisfaction, though hardly bliss, in her third.

She was denied the university education she craved, separated from her twin during three exiles, nearly lost one of her sons through bone disease, contracted tuberculosis herself, was almost killed in an assassination attempt and, last December, received a telephone call from her daughter in Paris saying that her son, Shahriar, had been murdered in the street.

One of the book's most interesting apsects is its portrayal of the relationship between Princess Ashraf and the shah -- the faces in the mirror. Her insights will be of interest perhaps to psychologists as well as to students of royalty and international affairs. In one of the rare emotionally charged passages in the memoir, she declares:

"No matter how I would reach out in the years to come -- sometimes even desperately -- to find an identity and a purpose of my own, I would remain inextricably tied to my twin brother. I would marry more than once. I would have children of my own. I would work for my country in ways unheard of for a woman of my generation. . . . But always the center of my existence was, and is, Mohammed Reza Pahlavi."

While there is no doubt she exerted a powerful influence over her brother -- the European press called her the "Black Panther," a name she did not dislike -- it is still unclear how much she actually guided his hand at critical moments. At the times of the greatest danger during his reign -- the Mossadegh crisis in the early '50s and the outbreak of revolution in late 1978 and early 1979 -- she was out of the country.

She describes her emissary's role in "Operation Ajax," the CIA's successful campaign to destabilize prime minister Mohammed Mossadegh, when she took a letter to the shah that had been given to her by a mysterious American and an Englishman in Paris. However, she says she cannot reveal the contents of that "fateful letter," although it is hard to believe that whatever it contained would have added much to what the United States and British governments were telling the shah through their own secret channels in Tehran.

Accusations of corruption, greed and drug trafficking dogged her as the shah grew more confident, helped by the brutal SAVAK -- an organization Princess Ashraf disingenuously claimed was "no worse" than the Israeli, French or British counterintelligence agencies -- and as his court glittered unashamedly in the exercise of unfettered power and in the riches of the oil boom. She denies these charges, and recalls that she successfully sued Le Monde for publishing a story about her smuggling heroin into Switzerland. Damages were awarded and the newspaper published an apology. She also obtained an apology from The Washington Post for publishng similar allegations.

Princess Ashraf's analysis of what went wrong in Iran is only partially convincing. Active all her life in the emancipation of Iranian women, she correctly highlights the upheaval that Western education and life styles in Iran caused among traditionalists such as the Moslem clergy.

But she underestimates the forces of constitutionalism which, basing their legitimacy and their hopes on the 1906 constitution, regarded the Pahlavis as usurpers and strove unavailingly to curb the powers of the monarchy. She aslo virtually ignores the crucial roles of the bazaar merchants and the middle-class technocrats in making the revolution possible.

The former funded Khomeini and his followers while the latter kept the country, including the vital oil fields, running during the year of turmoil that led to the shah's downfall. Against this powerful coalition there was little the United States or any foreign power could do to save a man who had become disastrously remote from his people.