Underlying the latest crisis in the Mideast negotiations is s strategic flux that affects this whole part of the world. The trouble begins with the semi-downfall of the shah of Iran, then spreads through Iraq and Syria to Saudi Arabia, which bounces it back to the talks between Israel and Egypt.

American understanding of this geopolitical shift is critical. For the change undermines, and perhaps even destroys, the set of ideas about oil, Israel and the Arabs that has guided American foreign policy in this part of the world since 1973.

Nobody yet knows the final outcome of the difficulties that have erupted in Iran and threaten the throne. But internal problems now monopolize attention in Tehran. The shah cannot for now and probably for a long time to come, if ever - be the dominant figure in the Persian Gulf.

The radical regime in Iraq, which has long been held in check by the shah, has drawn the appropriate lesson. Iraq has now reentered inter-Arab politics as an active player. A first sign was the rapprochement, and establishment of a joint command, with Syria. A second was the Arab summit meeting in Baghdad.

Saudi Arabia is affected by those developments in many ways. The weakening of the shah removes a relatively benign protecting power and gives heightened importance to the potentially subversive Iraqi influence in the Persian Gulf.

Reconilization between Iraq and Syria further embarrasses the Saudis. IN the past, they could resist the appeals of each state by pointing to their division. But a joint call for help in Arab affairs meshes perfectly with the Saudis constant plea for pan-Arab unity. Thus trapped, the top Saudi leader, Prince Fahd. after musing about non-participation, finally felt obliged to attend the baghdad summit.

Once there he was subjected to pressure from all the Arab radicals, including the Palestine Liberation Organization, to take a stance against Egypt and its dialogue with Israel. Temporarily, at least, Prince Fahd gave way. Saudi Arabis has endorsed a condemnation of the Camp David accords that set up the Egyptian-Israeli talks and agreed to pay subsidies to those Arabs - notably the Syrians, Jordanians and PLO - who are standing aloof from the peace Eyptian President Anwar Sadat, with whom I was talking when the news came in, completely by surprise. Previously he had made no serious effort to win Saudi support for his talks with Israel. Thereafter he felt obliged to demonstrate that he was not, as his Arab opponents charge, advancing Egyptian interests at the expense of their claims on Jerusalem and Palestinian presence in the Gaza Strip and the Israeli-occupied territories west of the Jordan River.

Accordingly, Sadat first began insisting upon an operative connection between his deal with Israel on the Sinai Desert and the other Camp David agreement covering the West Bank and Gaza. To prove his seriousness - to show the other Arabs that he was in fact pushing Israel all the way back - Sadat then sent his vice president, Hosmi Mubarak, to Washington with a proposal that Egypt be given a presence in the Gaza Strip.

With the Egyptians moving to remodel the Camp David accords, the Israelis have held off making any decision. Their hope was that Washington would reject the Egyptian demands. Since Washington hasn't, the Israelis probably will.

Eventually though, some kind of compromise can eventually be struck between the Egyptians and Israelis. Both governemnts have gone too far down the road to settlement in Sinai to turn back now. Moreover, many of the components of the shifting geopolitical scene are subject to further change.

The shah can be propped up some. More steel can be put into the Saudi backbone, especially if President Sadat is more careful not to offend Saudi sensibilities.

But the critical point is that Washington take into account what has happened here. The example of Iran shows that the conservative oil states of the Persian Gulf are vulnerable to internal opposition generated by the unequal distribution of vast new wealth. Like Iran, Saudi Arabia and the Persian Gulf sheikdoms are intrinsically unstable.

They cannot be made amenable for further export of oil to Europe, Japan and the United States by forcing Israel to make peace. The Arab-Israeli quarrel, in other words, is largely separate from oil politics. Like most of the "big think" conceptions of the foreign policy establishment, the notion that pushing Israel to accept a pro-Arab peace will guarantee access to oil has been proved wrong.