Egyptian President Anwar Sadat's declared readiness to visit a land that does not even exist on Arab maps or in Arab textbooks is a bold break with some major taboos in Middle East mythology.

Arab cartographers and school teachers still deal with Israel as "Occupied Palestine." Arabs since 1948 have been conditioned psychologically to view the Jewish state as an outlaw creation doomed to disappear.

But the Egyptian leader has given the Middle East a new jolt of his own brand of psychological "shock treatment" by publicly soliciting an invitation to go to Jerusalem to put his case for a negotiated peace to the Israeli Knesset (parliament).

Jerusalem is one of Islam's three holiest cities and Sadat is pledged to regain the Arab sector in any peace agreement.

In American terms, his decision is even more dramatic than President Nixon's 1972 trip to mainland China. The most exact equivalent would be a decision by an American President in the coming years to visit Communist-ruled Saigon.

"Shock treatment" is the phrase Sadat used to describe his decisions to expel Russian military advisers from Egypt in 1972 and then to go to war with Israel in 1973.

Sadat explained that each of those decisions, which initially stunned his own populace as well as the world, were intended to break diplomatic and psychological stalemates.

They eventually emerged, however, as meticulously prepared moves in a larger strategy that Sadat has doggedly followed, and which he says will eventually lead to a peace with honor between the Arabs and Isral.

Despite the improptu appearance of Sadat's remarks to traveling American congressmen about visiting Israel and the subsequent television pairing of Sadat and Israeli Prime Minister Menahem Begin, diplomatic analysts said yesterday that Sadat again appears to be acting according to a carefully laid game plan.

The quick, precedent-shattering exchange via media also indicated that Sadat has found in Begin and Israeli leader who shares the Egyptian's decisiveness and appreciation of the drama of politica and diplomacy.

The two leaders were clearly aiming their words at American public opinion and were intent on showing that they do not want to be held responsible if the Carter administration's Middle East peace effort breaks down.

But they were just as clearly aware of the inevitable dramatic impact in their own region of their words, which add significantly to a new vocabulary that has been developing in the Middle East since the beginning of the decade.

For two decades after Israel was founded, Arab leaders, broadcasters and many average citizens refused to pronounce the word "Israel" in public.

Even after the crushing defeat of Arab armies in the 1967 war made many Arabs begin verbally to accept the reality of the Jewish state, all Arab leaders formally bound themselves to reject negotiations, recognition and trade with Israel.

Sadat has significantly changed the Arab vocabulary since coming to power in 1970, and evidently sees a gradual but steady change of basic psychology as an integral part of ending the state of intermittent war between the Arabs and Israelis.

He first surprised other Arabs 1971 by speaking of his willingness to make "peace" with Israel. His remarks, however, were derided as in sincere by Israel's Labor government which did not think they were wrong testing.

In the middle of the 1973 war, Sadat called a press conference to disclose that he had gone to war to make peace. His call for serious peace negotiations opened the way for Secretary of State Henry A. Kissinger's "step by step" diplomacy and the two interim Sinai agreements.

His expressed willingness to meet personally with Israeli leaders - even if it is not carried out - is perhaps on even greater turnaround. Sadat has previously said that personal contacts, trade and fromal recognition of Israel were matters that would have to be worked out by "another generation" of Arab and Israelis.

Since Jordan's King Abdullah was assassinated in Jerusalem in 1951 after it was rumored that he had entered into secret contacts with Israeli leaders, Arab heads of state have refused personal contacts through a mixture of prudence, political theology and bargaining tactics.

In going to Israeli jerusalem, Sadat would be giving away a major Arabs bargaining chip. In the past, he has taken such steps as part of a "paying in advance" strategy and forcing the hand of his negotiating adversary.

But he is also evidently depending on one of the strongest cultural traits in Arab society to give him a fire break if he goes to Israel and does not achieve immediate visible success.

Arab leaders are well known for quarreling bitterly, even going to war with each other, and then suddenly coming together publicly to embrace and pledge undying brotherhood and fidelty. Sadat himself has engaged in such exercises with Libya's Muammar Qaddafi and Jordan's King Hussein.

Arab publics have become accustomed to discounting much of the ceremonial peace-making, which rarely changes the underlying hostility that leaders and countries continue to feel. Sadat's mission to Jerusalem, if it occurs, may be a test of extending that Arab tolerance to Israel.