COMES NOW Mohammed Anwar el-Sadat, a self-described "peasant born and brought up on the banks of the Nile, where man first witnessed the dawn of time," to present us with his folksy account of the progress from that humble beginning to the day last November when he stood in the Israeli Knesset, furiously mopping at beads of perspiration forming around the smooth dark Moslem prayer mark on his forehead and transfixing the world with his speech as no leader had done since our own Richard M. said his tearful adios, amigos and headed off to San Clementa.

The elegantly dressed, soulful Sadat that the world saw last November in that television extravaganza was an entirely different Arab than most of the audience was prepared to see. That, in fact, is the ultimate point, both of the Jerusalem speech and also of releasing this book in America. Almost singlehandedly Sadat has set out to change how you think about Arabs. He is sneaking about with knives in their teeth and treachery in their hearts.

Fortunately, there is more in this tale. Sadat has lived a full, remarkable life, which he recounts in a humorous, emotional and very Egyptian spiel that is heavy on showmanship, momentously inflated in parts and subtly but seriously all business in other portions. It is the kind of artful weave of fact and not-quite-fact that is an Egyptian specialty.

The fun comes in following Sadat from the Nile-side farm into the Eyptian army, where he turns into a full-time conspirator and a part-time bungler, on into the prison cells that are his reward for the bungling, though his brief careers as rewrite man for a Cairo newspaper and saleman of bottled water, back into the army and eventually into a share of power and a nest in the giant shadow of Gamal Abdel Nasser for 18 years.

The obscurity that Sadat accepted in the Nasser years was not fun; but it was safe. Sadat makes a point to tell us that he was the only man who never quarrelled with the headstrong Nasser, out of loyalty. His attacks here on his predecessor are bitter enough to sugguest that Sadat's knack as a survivor was perhaps more important.

When Nasser died in 1970, Sadat took over a demoralized Egyptian government with an empty treasury, no prospects of significant aid and a troublesome alliance with the Soviet Union. "All that we received from the outside world was abuse," he says accurately. The betting in Cairo cafes where Sadat was derisively called "Nasser's Pet Poodle," was that the new "Rais would not last a year.

Sadat has now ruled Egypt nearly half as long his predecessor's heavy political legacy with surprising ease. Surprise has been the only constant of Sadat's reign. He has plunged into world politics with an elan, skill and elegance that have made him the grand master of international political drama and image-building.

Limited as it is, this interim autobiography helps explain why, and how. It is not primarily valuable as history, since Sadat has covered much of the same ground in his epic speeches to Egyptian political gatherings. It is a political document, one that resembles a campaign biography. In Sadat's case, the campaign is to win over American public opinion, and the book is angled to do that.

"Now that I have met President Carter. I am very optimistic," Sadat reassures any worried readers. Carter is "a man impelled by the Power of religious faith and lofty values - a farmer, like me." (Nixon, the beneficiary of such plugs during that Impeachment Summer of 1974, doesn't rate a mention in this volume.)

Sadat is indeed a farmer like Carter. He also leaves the farm as soon as he could for an appointment to the Royal military Academy and the life of an officer. He finds he intensely hates English colonial rule and tries to cooperate with the Germans in World War II. In the kind of unsuppressed anecdote that brings Sadat alive, he acknowledges that he got linked up with Germany's two clumsiest spies, who set up their radio transmitter on a houseboat parked next to Cairo's best known belly dancer and a friend of British intelligence.

Young Sadat beats a spy rap by metaphorically throwing dust in the eyes of his opponents and confusing them so thoroughly that they just give up. But he winds up getting arrested again in 1948 for plotting against King Farouk, and spends eight months in Cell 54 in Cairo Central Prison. His stay in Cell 54, he explains each time that he has to reach a hard decision like throwing out the Russians or going to Jerusalem, was the turning point in his life, giving him a mystical kind of self-confidence and a "talent, or capacity, for change." Now he can throw away any central premise and reorganize the sitution anew.

But jail does not improve his timing. Reunited with Nasser and the other officers plotting the 1952 revoluation, Sadat goes off to the movies on the night the coup is launched and he misses the crucial first hours. They begin the revolution without him, but he catches up, endures the next 18 years as a second fiddle to Nasser and, like Claudius on taking power, transforms himself from a laughingstock into a truly bold, imaginative leader.

The few new historical nuggets Sadat offers suggest that his actions are far more calculated than their hasty execution makes them seem. He gives the most detailed account yet of how the Nixon-Brezhnev detente communique of May 1972, and the resulting Russian restraint in delivering arms, led directly to Sadat's decision to expel the Russian military experts in July, 1972.

His account of the October War in 1973 is just not believable in parts, especially on the Israeli breakthrough across the Suez Canal in the war's closing days. Sadat goes on to quote a conversation with Henry Kissinger that is unconfirmed but has a certain Kissingerian ring to it. Kissinger is discussing the global military alert that Nixon called on October 25 and reportedly warns Sadat that American forces "planned to land in your country, in Sinai, if the Russians landed west of the Canal, to finish you off . . . the Pentagon wants to avenge the defeat of [U.S.] weapons in October" by Russian weapons.

Sadat does not spell out where he intends to take his peace effort now, but he puts emphasis in the concluding part of his book on the idea of a defense pact between Israel and the United Sates that would cement a final peace accord. In theory, such a pact would establish an American veto over Israeli attacks on Arabs as well as defending the Israelis from Arab aggression. Direct involvement by the United States also could reduce popular pressure on Arab leaders to start a future war with Israel, as suggested by Sadat's argument during the 1973 conflict: that he could fight Israel but not Israel and the United States together.

"Never make the mistake of thinking that Sadat has played his last card," a member of the Saudi Arabian royal family advises. "He's always got one more hidden away. The secret of his strength is that hidden card."

Running though the autobiography is a subdued hint of what may be Sadat's last card if the peace initiative fails. Sadat presents himself as feeling "far above the petty conflicts" of governing and merely holding power. The last card in the hole for Sadat is resignation. It is a card he would play reluctantly, but with his typical verve and delight in turning the Middle East upside down.