THIS COULD HAVE been a marvelous book. It could have presented the insights and counsel of the man who has, after all, the world's best credentials as a Middle East peacemaker. Or -- no less intriguing to president-watchers -- it could have presented the candid latter-day reflections of the man whose greatest achievement, the peace between Egypt and Israel, may, he indicates, yet unravel and which in any event did not become the grand and comprehensive Israeli-Palestinian settlement that plainly was his heart's desire.

Unfortunately, this is neither of those books. It has passages of great interest and ideas of great merit but it is part travelogue, part textbook, part memoir, part policy paper, and finally none of the above: a flatly written statement that left me wondering why he did not have an editor with the elementary sense to demand that he write his best book, and how difficult it must be to be Jimmy Carter.

The book begins with some ideas, which I read three times and did not understand, about Arabs, Jews and Moslems all sharing the blood of Abraham. But okay, I said to myself, I always figured Carter had a religious calling to bring peace to the Holy Land. Unfortunately, this sternly self-disciplined man does not really close with the vital matter of his motives. His brooding, it seems, is private. There is scarcely a note of introspection evident throughout the book.

I think this is critical. The question of Carter's personality, his psyche, has got to be controlling for his view of the Middle East. It was what drew him to the problem and what made him so patient, understanding, insistent and resourceful -- so superb -- as a mediator. The evidence of the public record, including this book, is that the personal factor has kept on affecting his thinking since his days of triumph.

It appears to me that at some point during the Camp David process, something snapped in Jimmy Carter, turned him sour, specifically, turned him sour on Israel. I suspect it was a string of outrageous steps taken by Menachem Begin -- exploiting Carter, taking advantage of his every generous impulse, squeezing him beyond human endurance -- culminating in the dispute that Begin won over suspending new settlements in the West Bank. Thus was lost what slim, crazy but real chance there was to start to draw in the Palestinians, and once it became clear that the Palestinians were going to stay out in the cold, the Egyptians were bound in time to start losing the faith that Carter had evoked to bring them aboard.

I say Carter soured on Israel. I think he also sweetened on the Arabs. The evenhandedness he professed and practiced while in power has since yielded to a scarcely concealed onesidededness. Carter's writing now conveys an unmistakable sense that the plight of the Palestinians is paramount in his mind, touches him to the moral quick, that Israel is responsible for the Palestinians' continuing tragedy, that Israel has fallen from grace. He can write of, for instance, the Saudis, whom he sees as "a crucial and beneficial force" for peace, that although they "look upon Israel as a disturbing irritant that might ultimately be removed, in the meantime they would probably give tacit support to a peace arrangement based on U.N. Resolution 242 or the Fez declaration . . ." No less chilling than his picture of the Saudis is his evident unawareness of how chilling that picture is.

IF YOU HAD the world's sweetest prize almost in your grasp and someone took it from you -- or that is what you thought, anyway -- would you not harbor just a bit of bitterness, just a bit? Of course Jimmy Carter, still in his heart the Christian soldier marching toward peace, does not blame Begin or the Israelis outright. One can guess it is painful to relive the story in detail. There evidently is not available the documentation to match that which the Israelis provide to support their case on the settlements. Carter is in deep repression on this most crucial episode. It imparts to his book its strained clenched-teeth quality, as though he is not levelling with himself, or with the reader.

Carter is too intelligent, knowledgeable and decent not to make the obligatory bows to everybody's responsibilities to peace. But there is more weight to his collateral asides and indirect statements to the effect that the Israelis fling their political weight around in the United States and the United States must lean on them if they continue to reject the legitimate demands of the Palestinians.

All of which has much truth. The Israelis do fling their political weight around, brazenly, and the United States should not hesitate to lean on them, wisely. But this is truth on the second level, not on the first level, where it counts. Carter worked on the first level at Camp David. He succeeded there not simply by leaning on the Israelis but by seizing an historical opening, by grasping the psychology of two unique men, and by demonstrating an empathy for both nations' most profound anxieties, Israel's about its future -- survival, Egypt's about its past -- pride.

At Camp David, Carter did not threaten Israel with punishment, loss and abandonment in the name of overarching American interests, which is, I think, the direction his tone now points to. Such a strategy is wrong and cannot work on a determined sovereign state with the resources at Israel's command -- resources, including its political clout, that cannot be disposed of by sticking pins in a phantom Begin doll or by performing prodigies of manipulation and maneuver, although prodigies are necessary.

Carter forgets that Israel has a perfect batting average on negotiations: two for two. No one who ever sat down with Israel has gotten up without feeling utterly battered but ready all the same to sign on the dotted line. Afterwards, with both Egypt and then Lebanon, deterioration set in. That is something for Israel and its friends to think about much more seriously than they have. But agreement was reached.

The way to get peace in the Middle East is to put a reliable Palestinian at a table opposite Israel. In the right circumstances, it could even be Yasser Arafat: the ultimate Israeli objection to him is less that he leads a band of "terrorists" than that he cannot deliver the people he claims to represent. Then send over an American mediator who has the moral and political stamina Jimmy Carter brought to Camp David. There's peace for you.