Behind all the emotion and excitement that has built up here over the arrival of Egyptian President Anwar Sadat in Isreal today, there is also an atmosphere of apprehension and a realization that the politics of the Middle East may never be the same again.

Sadat is not coming to negotiate a separate peace with Israel and Israel will not press him to do so. Prime Minister Menahem Begin had said that the positions he presents to Sadat "will not necessarily be new ideas."

But as Foreign Minister Moshe Dayan told a group of visiting American congressmen this week, "The crucial question after Sadat's visit will be where do we go from here?"

"The world will expect us to make the next move," said Meir Amit, Israel's minister of transportation and a former head of the Israeli intelligence service. "If we fail, we may face a situation far more dangerous than before." There is a feeling that it will be impossible to let Sadat return to Egypt completely empty-handed. But at the moment Israel is in a quandary as to how to respond.

Equally significant is the fact that in this precedent-shattering visit, Sadat has badly jolted a long-held Israeli conviction that the Arabs could not accept the idea of a Jewish state in their midst and therefore, when all was said and done, peace was impossible. It did not matter how Israel might long for peace or what Israel offered. The Arabs simply couldn't accept Israel.

This perception became a security blanket and a crutch. For if peace with the Arabs was not really possible anyway, then Israel did not need to do anything but hang on and try to outmaneuver the Arabs politically or beat them in war if push came to shove.

The reaction against Sadat's visit in much of the Arab world will con vince Israelis that the theory is not completely outmoded. And 10 years ago, when Arabs got together in Khartoum to declare: "No peace, no negotiations, no recognition of Israel," there was more than enough evidence to support the contention. But the arrival of the president of the most important Arab country, on what amounts to a state visit, will now force many Israelis to reconsider many basic convictions. As one political observer said: "Ideas that were perfectly acceptable in the past no longer fir the new circumstances."

The Egyptians have long felt that every time their president made a move toward de facto recognition of Israel, the Israelis simply put the concession in their pocket and said it wasn't god enough. But the Sadat visit is such a bold move and such and extraodinary gamble that Israelis cannot simply sit back and say that nothing has changed.

The three noes of Khartoum 10 years ago have now become the three yeses. Sadat is saying to the Israelis: But you must withdraw from occupied territories on all fronts and you must make some provision for a Palestinian entity. If not, the moment for peace will pass and the Middle East will slip back in war.

And although Israel has perhaps never been more powerful militarily in relation to her enemies, there is a growing realization here that Israel cannot really win another war politically, and without a political victory a military victory would be meaningless. Military planners dismiss the concept that a strong Israeli attack could set the Arabs back 10 years. Even the most crushing defeat of combined Arab armies would mean only a brief respite of a couple of years at the most, as the Arabs could quickly resupply.

The political liabilities of another oil embargo, isolation from the United States and, in all probability, a massive return of the Soviets into the Middle East arena would make the military victory hollow and meaningless.

But, as Moshe Dayan has pointed out, Sadat may be sincere in his desire for peace, but who will follow Sadat? Israel feels it cannot give up tangible territory for intangible peace promise; that could be broken. That is why Israel insists on a peace that would bind the Arabs.

Today it is the Israelis who have their three noes: no negotiations with the PLO, no foreign control of the occupied West Bank and Gaza, and no return to 1967 borders.

The Sadat visit is going to bring pressure upon Israel to soften, if not abandon, some of their noes. But as Sadat has said, the real problem in the Middle East is the psychological problem and the real meaning of the Sadat visit will be that Israel will have to re-examine its own heart.

Although there are many Israeli families who have lost sons in four wars against Egypt and other Arab states, there have been no demonstrations or protests in Israel against the Sadat visit. "If Sadat's mission does not open a developing dialogue with the Arab world," an Israel social scientist said today, "the anguish of these families will become that of the entire Israeli public . . . Rebuff from the Arabs could be catastrophic in a way that the Arabs and the Americans may not understand. If Israel is pushed back into paranoia it may well become a "crazy state beyond control." Israeli leaders know that great expectations have been raised in Israel and that besides the great chess game of international Geneva diplomacy, there may well be a domestic political dynamic at work here that may effect the future of the country for good or evil. That is why there is so much conern in Israel tonight as to how to meet the challenge Sadat has flung at Israel's feel.