The scene was Anwar Sadat's palatial retreat, 20 minutes outside of Cairo. The garden gate was guarded by a lone soldier. There was no one else in sight--other than a lanky figure in a dark blue suit, stretched out on a lawn chair some 50 yards away, reading a book and sipping iced tea.

As I approached, the figure rose, stepped forward and introduced himself: "My name is Anwar Sadat." Apart from the brief appearance of a photographer, that was the extent of the ceremony. My first and lasting impression of the president of Egypt, then, was that he was an unpretentious man; my second (equally enduring) impression, from what he had to say in a taped interview lasting more than an hour, was that here was a man with a vision that went far beyond the politician's obligatory protestations of a desire for peace.

That was in February 1975, when Henry Kissinger was in mid-shuttle, a reconvening of the Geneva conference on Middle East peace was the commonly accepted goal, and the celebrated visit to Jerusalem was beyond anybody's wildest dreams.

Everything that followed, of course, has confirmed that first impression, making it all the more tragically ironic that Anwar Sadat should have died in the pomp and circumstance of a military parade.

This is not to lay claim to some special insight; the glimpses of what was to come, at Sadat's hands, in the shaping and forming of a "peace process" culminating at Camp David, was in his message six years ago.

Did he "foresee the day when Egypt and the Arab countries can really coexist with Israel and have free cultural and economic exchange?" Sadat was a visionary without illusions: "You are asking the impossible now." What he was pleading for, urgently, was for "our generation to end this state of belligerency." The coming generation would have to work out the rest.

And what he was looking for, he said, was nothing so fanciful as immediate, simultaneous Israeli withdrawal from all the occupied territory: the Sinai, the West Bank, the Golan Heights. What he wanted was an agreement "on principle that this would happen. Then it can be worked out, I mean one by one, okay."

Time, he thought, was on the side of peace. Egypt had suffered mightily since the 1967 Six-Day War. More than $1 billion had been spent on the armed forces which should have been used for domestic needs. He foresaw negotiations with Israel, "but if a third party can come in between to guarantee both of us in the process of negotiations--very well."

He had firmly in mind as "third party" the United States, in the form at that time of his "friend Henry" Kissinger. His "friend Jimmy" Carter was not yet on the scene.

Recalling all this, reviewing Sadat's extraordinary performance in the intervening years, remembering him now as a charming, driven, larger-than-life genuine world statesman, is to be tempted to a quick conclusion: Sadat is irreplaceable; no successor can fill this void. The kaleidescope has been given one more cruel turn, and the Middle East mosaic will never be the same. It is hard to argue otherwise, and harder still to hope that somehow the processes now at work--the so-called autonomy talks for the West Bank (Sadat's second step as far back as 1975) and the final arrangements of the Egyptian-Israeli peace treaty-- can be successfully carried forward.

There will be hitches, certainly. At this writing, it is not even known who will succeed Sadat. Speculation centers on Vice President Hosni Mubarak, of whom one authority said, "Even those who know him don't know him." He is an air force general, with strong military support. He is also described as "Sadat's clone" by a student of Egyptian affairs, who quickly adds that "this tells you nothing of how he might act alone."

So my advice is very simple: it is very nearly useless to speculate at all. There will be uncertainty, perhaps even a vigorous power struggle, lasting for months; first impressions are almost certain to deceive--if past history is any guide. On that score, the record is clear.

When the cabal of colonels overthrew Egypt's King Farouk in 1952, the unmemorable Gen. Muhammed Naguib emerged as at least the nominal head of the resulting governing junta. John Foster Dulles took him seriously enough to pay a visit and present him with a plated .38-caliber pistol as a gift from President Eisenhower--one general to another, so to say. Gamal Abdel Nasser was to emerge as the real strongman only after many months.

And when Nasser died in September 1970 his successor was regarded by knowledgeable State Department experts as something of a clown-- Sadat was the least impressive, it was said, of the organizers of the coup against Farouk. As Henry Kissinger is frank to confess in his memoirs, when a journalist asked him his opinion of Sadat, "I said I thought he was an interim figure who would not last more than a few weeks--that was among my wildest misjudgments."

If that suggests some reason to withhold judgments now, there are some forces at work that argue for a degree of continuity. The Egyptian establishment, however that may be defined precisely, and the Egyptian public want the Sinai cleared of Israeli occupation. Only Israel can deliver on that. Israel's Prime Minister Menachem Begin wants "full normalization" of relations with Egypt, not just a peace treaty on paper. Only Sadat's successor can deliver on that.

There are reasons, then, for expecting both sides to press on with the peace talks, and perhaps even Camp David as well. The so-called Framework for Peace is as much Begin's monument as Sadat's (and Jimmy Carter's). To scuttle the autonomy effort, so recently resumed, would be to put at risk the complettion of the Israeli-Egyptian peace talks.

But we aren't going to speculate. Thequestion marks are enormous, and no more so than in the strategic relationship the Reagan administration had been so carefully cultivating in the region with Egypt, Israel and Saudi Arabia as the cornerstones. The origins of the assassination, just to begin with, remain obscure.

Obviously things are never going to be the same. A very large figure has left the scene. But only time will give us a true measure of how great the differences will be.