WHY ARE we still musing about the character of Richard Nixon? If we can repress the Vietnam war and pretend it never happened, we certainly ought to be able to do the same with him. But apparently it's not so easy. Nixon, restlessly prowling around the country in a quest for rehabilitation, keeps turning out books, while others turn out even more about him. The public seems to have as insatiable an appetite for this material as it does for miracle diets.

The reason we can't put Nixon to rest may reveal as much about us as about him. Lacking the useful figurehead of a well-meaning and dimwitted monarch, we deify our presidents, expecting them to behave like the paragons we want rather than like the politicians they are. Naturally we are shocked when a devious congressman or governor turns out to be no less devious on becoming president. In America the president is not just the biggest enchilada, but the very symbol of national unity. Whoever holds the office is the keeper of our dreams as well as of our needs. No wonder that he soon disappoints, and a little later disillusions, us. Only martyrdom, as in the case of John F. Kennedy, or the soothing balm of time -- witness the recent resurrection of Harry Truman and Dwight Eisenhower -- allows our wishes to triumph over our memories.

No doubt Richard Nixon, too, having had a spate of deserved comeuppances, will be resuscitated by future historians now in toddling clothes and enshrined in the same pantheon with the vulgar Truman and the bumbling Eisenhower. In the meantime we continue to wonder why it was that he didn't live up to our image of what a good president ought to be. The reason, we assume, must be some terrible, and of course well-concealed (that is, until Watergate) flaw in his character. Thus it is that over the years we have had a tide of books seeking to unravel the mysteries of Nixon's character -- though one of the first, Garry Wills' stunning Nixon Agonistes, still remains by far the best.

Now Fawn Brodie, a distinguished historian at UCLA until her death early this year just after completing this book, offers another variant. Brodie, it will be recalled, several years ago shocked worshipful Jeffersonians with her allegations of the paterpatria's dalliances with his black mistress. Here her target is more assailable, since Nixon is obviously the man we all love to hate -- especially since we once gave him our love with one of the biggest electoral majorities in American history. Now he is a pariah, but hardly an unmentionable one. Why does Nixon continue to arouse our anxieties, she asks. Because he reminds us of our own lies. "We need reassurance that his lying is pathological whereas ours is simply 'white' lying."

Curiously Brodie sets herself the task of providing precisely such reassurance. The key to Nixon's character, we are told, is a compulsive need to lie. Unlike the rest of us, Nixon lied not only when it was useful, but because it gave him pleasure and kept his bruised psyche well-oiled. "You don't know how to lie," she quotes him telling an anonymous friend. "If you can't lie you'll never go anywhere." Sound advice in politics, one would assume. But for Brodie this is evidence of a warped character and an "identity failure." Nixon, she insists, "lied to gain love, to shore up his grandiose fantasies, to bolster his ever-wavering sense of identity." The sheer quantity of the lies suggests to her a "pathological origin."

Employing some of the jargon and much of the method of psychobiography, Brodie digs into his past and finds the usual traumatic childhood: a stingy, brutish father and a "saintly" mother who punished by withdrawing love; parents who nourished his ambition but "starved his soul." Naturally the sense of being unloved, if that is indeed what young Richard Nixon felt, led to "self-loathing" and to an all-consuming "fantasy life" in which "ever-greater glory and ever-increasing power became the most powerful motivating force in his life." Applause, though it could not appease the self-loathing, could drown it out. And thus it was that Nixon, though a part of him sincerely wanted to bring truth to government and peace to the world, lost touch with reality because of his own internal need to deceive. When lying failed to work, as in the last days of Watergate, insecurity gave way to "paranoia."

Continued exposure to the jargon of psychiatry has inured us to this kind of long-distance literary psychoanalysis. One can hardly say that it is wrong. Who knows? Maybe Nixon did suffer the primitive certainty of being unloved and unlovable" and thus was consumed by a "self-loathing" that could be assuaged only by deception, power and applause. But a decent respect for the mysteries of the human soul also requires one to observe that many people with noisy fathers and mothers with tainted halos do not become pathological liars, let alone president of the United States. To be sure, Nixon later described his childhood as being sunnier than it probably seemed at the time, or than Brodie's account reveals. But if this be psychopathology, Nixon has a lot of company.

Brodie makes a good deal of the theme of "fratricide" in Nixon's life. From the fact that two of his brothers died in childhood -- one from tuberculosis, the other probably from an accidental wound -- she concludes that his fate is somehow linked to that of brothers. As evidence she cites his attacks on Communist spy Gerhart Eisler and his brother Hanns, on Alger and Donald Hiss, on Fidel and Raul Castro, and on the Kennedys. She does not mention whether Ho Chi Minh had a brother. But she does maintain that almost all of Nixon's victories were "won as a result of lying attack or the unexpected and fortuitous death of others." It is hard to know what conclusion to draw from such a statement, particularly since Brodie herself confesses that the theme of fratricide leaves her "baffled and anguished." It is unfortunate that she did not resolve the bafflement before drawing inferences. If Nixon benefited from the death of others, how about Lyndon Johnson, or Theodore Roosevelt, for that matter? "Fratricide" should be forged from sterner links.

Although Brodie's book has enough anecdotes to keep a Nixon-hater in ecstasy all year, it fails to do justice to the full complexity of her subject. As Brodie herself points out, and then largely proceeds to ignore, Nixon was two people -- and I don't mean a schizophrenic. He was enormously ambitious and would say anything to win an election, as his vicious campaigns against Jerry Voorhis for the House and Helen Gahagan Douglas for the Senate demonstrated. But he was also an idealist whose political hero was Woodrow Wilson and who wanted to be remembered as a great president. It was the ambition, not the lying, that was central. He had a consuming need for applause and ego gratification. What politician or actor doesn't? But what is interesting about Nixon is that he wanted to do something that would allow him to be revered by future generations. He wanted to be Woodrow Wilson. And in one respect he was, for he engineered his own failure at Watergate just as surely as Wilson did over the League of nations. A study of Nixon that does not deal with this dichotomy -- and Brodie touches on it only lightly -- does not do full justice (if that is the word) to the complex character of its subject.

Although psychobiography can, in very skilled hands, stimulate revealing insights, it also poses yawning pitfalls. The most obvious is the interpretation of data. Brodie tells us, for example, that Nixon's reluctance to watch himself on television revealed a "continuing dislike of his real self." Could it conceivably have been modesty, or even, since he had been on television many times, that he had better things to do? And, for that matter, is television the "real self"? Seeing psychological aberration in every action, Brodie makes Nixon seem so psychopathic that he can hardly be held responsible for his own actions.

For all its easy attitudinizing, Brodie's book offers a good deal of information, especially on Nixon's childhood and youth. The second half of this unnecessarily long book is far less interesting, going over familiar ground and often, in setting the historical stage, even losing sight of the subject himself. It would have been better as a short, daring, and highly opinionated assault. But having decided to be thorough, Brodie was not thorough enough. The important question is not why Nixon lied, but why he was not the president he wanted to be. After Nixon's resignation Henry Kissinger reportedly said that he had "never known another man who combined such great gifts with such a capacity for depravity and such a drive toward self-destruction." Brodie underlines the depravities, but mostly ignores the gifts and never really explains the self-destructiveness. That -- not the lying -- is the fascinating part about the remarkable Richard Nixon. And that is the book that has yet to be written. CAPTION: Illustration, DRAWING BY DAVID LEVINE. Reprinted with permission from the New York Review of Books. Copyright (c) 1974, Nyrev, Inc.