AT THE RISK of delivering something that sounds like a position paper for a symposium, we would like to offer a few rather elementary thoughts today about the Nature of Negotiation - and the Role of the United States - in the New Midesat Diplomacy (with subsections entitled The Principle of Evolution and The Necessity for Ambiguity). We are driven to this dissertion, in part, by a fleeting exchange the other night between Barbara Walters and Egypt's President Anwar Sadat just after the Aswan encounter between Mr. Sadat and President Carter. As between "self-rule" for the Palestinians and "self-determination," Mr. Sadat was asked, "Which did President Carter think was better?" Patiently, the Egyptian President replied: "They are not so different, Barbara" - and that is just the point. They are not so different; a limited system of self-rule, to be applied immediately, could be the logical first step toward an ultimate right to full self-determination, to be accepted in principle as part of a phased, long-term, comprehensive Mideast settlement.

But it is also true that in the course of their usage by one side or the other, these two phrases have taken on the freight of code words. To Mr. Saday, "self-rule," as proposed by Israeli President Menaham Begin, conveys the idea of limited autonomy and an indefinite Israeli military presence on the West Bank. To Mr. Begin, "self-determination" for the Palestinians conveys the idea of instant creation of a new, contiguous, sovereign and potentially hostile Palestinian state.

So the question is obviously not which phrase is "better" - at this delicate stage, given their loaded implications, both are unacceptable. That is the beauty of the careful language employed by President Carter, embraced by President Sadat (and not seriously objected to by Mr. Begin) after the Aswan meeting: "The parties must recognize the legitimate rights of the Palestinian people and enable the Palestinians to participate in the determination of their future." Note the relative freedom of action implicit in the familiar word "determination" but also the sense of some restraint conveyed by the word "participate." Note also the reference, without apparent offense to Mr. Begin, to the "legitimate rights" of the Palestinians. When that same phrase found its way into fall's controversial U.S.-Soviet statement on the guidelines for a renewed Geneva conference, it was regarded in Israel as an unfriendly act. But when it is employed today, in a fundamentally different context, there is no loud Israeli protest.

This is a nice example, we think, of the Principle of Evolution. Without the Sadat initiative, with its sweeping concession to Israel of Egyptian recognition and acceptance, there could have been no breakthrough at Jerusualem. Without the Begin response, with its equally solid concession of some form of Palestinian autonomy on the West Bank, there could have been no advance to the Sadat-Begin meeting at Isamilia, and to the arrangement there of face-to face ministerial meeting starting Jan. 15. And without the Aswan meeting between Mr. Carter and Mr. Sadat, and the resulting agreement on a mutually acceptable statement of general principles, there would be little hope for substantive progress on the critical Palestinian question at the ministerial meetings. An evolving interaction between solid confidence-building concessions and widening, longer-range agreements in principle, with previous unthinkable things becoming suddenly thinkable - that is probably how the current negotiating process will continue to work, if it is to work at all.

The Aswan "communique," we think, is also a perfect example of The Necessity for Ambiguity - a certain measure of liberating ambiguity, if you will, to permit the parties to escape the entangling code words and proceed toward hard bargaining within a mutually accepted frame. And so we find it passing strange that President Carter should be under fire for contributing to the ambiguity - for talking too much, or without reflection, or inconsistently. Still odder is the suggestion from various quarters that he should choose sides or enunciate some finite U.S. "policy." Our own sense of it is that, now that the two principals are talking directly to each other, the United States can have no policy other than that of holding itself available as a moderator and conciliator when needed to help promote almost any agreement that the parties directly at interest can agree to. The American intervention at Aswan, it seems to us, suggests that the Carter administration, after a shaky start, is adjusting wisely, and constructively, to this new post-Jerusalem role.