The Mideast summit meeting projected for Camp David next month serves to keep alive negotiations between Israel and Egypt. Otherwise it is a high risk affair.

For the abyss yawns if the president's meetings with President Anwar Sadat and Prime Minister menachem Begin prove fruitless. But the record suggests that the Carter administration is too hooked on illusions of a comprehensive settlement and Israeli concessions to manage events in the Mideast effectively.

The evidence of these illusions is the administration abandoned the illusion of a comprehensive settlement only in part. When the president and Secretary of State Cyrus Vance finally saw what had happened, they took the view that any Israeli-Egyptian negotiations had to include an eventual understanding of what would happen to the West bank of the Jordan - a crucial piece of territory now occupied by Israel but claimed by the Palestinians.

Begians agreed not to assert Israeli claims to the West bank. But he refused to state explicitly that future control over the territory was open to negotiation. At that point the Carter administration began applying maximum pressure to force Israeli concessions. In effect, American policy was to push Begin from power.

That second Carter illusion ended when Walter Mondale visited Israel last month. The vice president reported back that Begin was solidly entrenched and not nearly so intransigent as imagined in Washington regarding the future sovereignty of the West Bank.

The administration then turned back to Sadat, and a third position. Mondale and special envoy Alfred Atherton pressed the Egyptian president to negotiate with Israel on the question of the West Bank five years from now. At a meeting with Israeli Foreign Minister Moshe Dayan at Leeds Castle in England in Mid-July, Egyptian Foreign Minister Mohammed Kamel apprently came close to accepting that formular for resumption of talks.

But not Sadat. Some of his other advisers and Saudi Arabia, which is basic to Egyptian finances, urged him to back away from the Israelis and link up with the other Arabs in a new, united front. Under their pressure, Sadat said he would not negotiate unless Israel accepted the yielding of territory as a precondition. Efforts by Atherton and Vance to win Sadat voer failed. So the United States abandoned its third position, and came round to the Camp David summit.

By any rational calculation, the Camp David meetings ought not to fail. President Carter's personal prestige is engaged, and, for once, he is in good position to apply pressure on Begin and Sadat. Neither the Egyptians nor the Israelis have any place to go if the talks fail. A very limited achievement - merely getting the talks going again - would be enough to make the Camp David meetings a "success."

The difficulty is that past experience may persuade Begin and Sadat that Carter is a patsy. Each may be tempted to think that by digging in hard he can get the United States on his side. So Begin will be loath to be explicit about territorial compromise, and Sadat will be unwilling to resume negotiation without some assurance of territorial gain.

Between now and the summit, accordingly, American diplomacy has to go all-out to prevent misconceptions. So advance preparations of the most detailed kind are required to ensure that both sides come to Camp David in a mood of conciliation clearly traced out. Most important of ali, Carter needs to clear his mind of cant about a comprehensive settlement and pressure on the Israelis. He needs to drive straight toward the only immediate practical goal: a separate peace betwen Israel and Egypt.