LO, THE WICKED Margaret Sinclair Trudeau. Or is she? After reading her supposedly scandalous book, Beyond Reason, I really think not. Flakeys, yes; wicked, no.

I suppose she shouldn't have written it just as I suppose Sheila Weidenfeld shouldn't have written her book about the Ford White House, First Lady's lady. Perhaps James Fallows should have kept his insider's opinions about Jimmy Carter to himself.

But there is another way of looking at these three now infamous revelatory peeks into the palace. Weidenfeld's book made the Fords look very appealing; her account of them could only enhance a Ford candidacy. Margaret Trudeau's book did nothing to alter my view of Pierre Trudeau except perhaps to make him seem even more attractive and interesting than I had supposed. Fallows' article about Carter was sufficiently balanced and judiciously devised so as to give Carter his full due while pointing out some important shortcomings in the man. The fusses being made over these works will eventually abate, and it is unlikely that anyone's political fortunes will suffer as a result of their having been written.

Yes, we must have standards, and no, it isn't nice to bite the hand that fed. But it is also critical to know something more than we are generally told about the men who have sought to rule over us and seek to still. For at the top-at the White House or at 24 Sussex Drive in Ottawa, as in other places of great power-there is this abiding intention: that the public know as little as possible about what is really going on, about how life is lived in democracy's courtyards.

As the youngest, most rebellious and most antic fist lady in history, Margaret Trudeau comes at us with such bemusing honesty and self-depreciation that we are offen set off balance no less than she. She was very much in love and, one feels, still is with the dashing "Christian philosopher-king" she married in a private church ceremony nearly eight years ago. She seeks to explain in Beyond Reason that whatever else was true about her life as Trudeau's wife (and much of it was happy), she was simply in over her head. She could cope one minute but not the next. She was a blissfully serene nurturer of babies and gardens on the one hand, but on the other a fretful, frightened fainter and screamer when the stress of her official role closed in on her.

She went off on sprees, had a nervous breakdown, felt she wanted to die. She feared and loathed first-ladyship much of the time and one can understand why: it is a life of appendageness, relentless, boring rituals, constant public scrutiny and an almost intolerable lack of personal freedom and privacy.

So in this demanding atmosphere, it is no wonder to me that such a young woman floundered and could not discover the essential truth about herself. Margaret recognizes, however, that she's a human swinging door, and gives us enough unwitting insights about herself to make it hard to resist playing armchair psychiatrist.

Margaret Sinclair was, in the first place, a daddy's girl. Growing up in the glow of Father's favoritism in a family of five girls, being the "cuttest" (as Margaret puts it), prepares one mainly for the effortless conquest of older men. It does not give one staying power or a sense of having to toe the mark in a mature relationship. At the end of the book, Margaret laments, "I spent an awful lot of time trying to please him [Trudeau], yet could never quite escape from my own romantic fantasy or the desire for a life very different from the one I was expected to lead."

While her husband sweetly forgave Margaret much post-adolescent flightiness (and even encouraged it at times), while he obviously reveled in her youthful beauty and style, while he rejoiced in her gift to him of three sons in six years, Trudeau's motto, "La raison avant la passion " ("reason before passion"-hence, no doubt, the book's title) got the best of him more often than not. And given the fact that he had lived by that motto into his fifth decade (he is now 59; she is 30), how could there not be tremendous areas of conflict? Not every couple with such an age span is Bogey and Baby.

Margaret, the self-proclaimed flower child, was hardly bent on upward mobility. She says of herself, "I was not so much a hippy as a failed hippy; a hippy without a cause." A middle-class '60s gypsy whose needs at the time she met the sophisticated Trudeau were contained in a joint and a knapsack. Hardly a classic wicked woman. Certainly not in a league with Wallis Warfield Simpson who disrupted royal succession.

Still, theirs is a love story and we all love a love story. Trudeau clearly abandoned reason for passion long enough to water-ski into Margaret's life on a Tahitian holiday, to sweep her up into a heady clandestine affair at his country estate and from there into a hush-hush wedding-one that, when made known, caused eyes to pop and roll all over the world.

But has anyone stopped to question seriously, amidst all the moralistic furor over Beyond Reason, why one of the linch-pins of world order courted for his wife in a Catholic country a Protestant flower child just out of college? Has anyone recently choked on the idea of a man in his knowing and worldly middle age escorting into the most high-pressured kind of political life a mate so young, so inexperienced, so unanchored as Margaret Sinclair when countless decorative and far more savvy and secure women were available to him? No. Margaret must take all the heat. She could not possibily be his mistake; she alone is responsible.

More than one of Margaret's many outraged critics in the press have charged her with shamelessly trading on her famous married name.Where and what would this dingbat be, they froth virtuously, without the name of Trudeau? Who would otherwise care? The answer is: no one, aabsolutely no one. But her name is Trudeau and she is still the legal wife of a prime minister of a vast nation. Therefore, people care.

The Trudeaus' unlikely pairing became kind of a collective public fantasy in which any average young woman might dream of meeting a handsome prince on water skiis in a tropical paradise, and a lonely middleaged bachelor could dream of a cozy old age adorned by a dazzling and devoted young girl. Margaret went and shattered that make-believe and that is her real crime, one for which she will not too soon be pardoned. CAPTION: Pictures 1, 2 and 3, Margaret Trudeau with Pierre and their three children (above), with Prince Charles (bottom left), and with Mick Jagger. Photographers from the book