EGYPTS PRESIDENT Anwar Sadat has let it be known that he wants President Carter to be a "full partner" in the Camp David summit meeting on the Middle East next month. And Mr. Carter has said that he's ready to accept that role. But Israel's Prime Minister Menachem Begin says he doesn't know what "full partner" means - which is another way of saying that he thinks he does know what it means and that it makes him nervous. "Honest broker" is the way Mr. Begin insists on putting it - that, and nothing more. On the face of it, it would appear that Mr. Carter has already taken Mr. Sadat's side on a procedural issue of some consequence to the outcome of the Camp David talks. Is there, then, the germ of a serious misunderstanding here? Or is it a semantic quible blown up into a big difference as part of the inevitable warm-up sparring before the main event?

The answer is that it's a little of both. There is almost certainly a significant difference in the Israeli and Egyptian perceptions of the appropriate level of participation by Mr. Carter in the actual negotiating process at Camp David. But the difference is one of degree, deriving, we suspect, from each side's current estimate of where the United States is likely to come down on the hard questions that divide them. Rightly or wrongly, the Israelis feel they've taken most of the American heat in recent months. That might be reason enough for Mr. Begin to want ground rules that would limit Mr. Carter's role at Camp David.

But there's a deeper reason, having to with Israel's particular - and justifiable - security concerns. Feeling themselves to be acutely and uniquely vulnerable in strictly military terms, they are understandably leery of being drawn into anything that even begins to look like an imposed settlement, and never mind who may be doing the imposing. What may be a matter of territory or national honor or politics for the Arab countries, they argue, is for the Israelis a matter of life and death and, therefore, something to be negotiated directly with their adversaries. So when Mr. Begin speaks of honest brokerage as the proper U.S. role, what he is really doing is trying to head off any American inclination to come up with its own comprehensive, compromise settlement plan.

For his part, Mr. Sadat has made it known that he would have considerable confidence in just about anything Mr. Carter might propose. His sense of it seems to be that the U.S. position is closer to his than to that of Mr. Begin; by his reckoning, accordingly, the deeper the U.S. involvement, the greater will be the U.S. pressure for concessions from Israel. Hence his emphasis on a "full partner" role for the United States.

The difference, in other words, is more than a matter of semantics; it is a question of tactics, of maneuvering for advantage in the lull before the talks begin.But as for its being a genuinely divisive issue, threatening the outcome at Camp David, we doubt that it will come to that, if only because we suspect that Mr. Carter is well aware of the pitfalls of overbearing intervention - or of anything that even smacks of a settlement imposed by the United States. The danger is not just that an American masterplan to bridge the gulf in a big and all-encompassing way might be rejected. There is an equal danger in its being accepted, grudgingly, under heavy pressure and in a way that imposes an inordinately heavy obligation on the United States to hold together an agreement for which the parties directly involved take no real responsibility.

Mr. Carter has almost said as much in talking about how he envisages his role. He has spoken, for Mr. Sadat's benefit, of being, an "active full partner." But he has elaborated, presumably for Mr. Begin's benefit, in a way that suggests a more modest, middle man's role, seeking to isolate areas of agreement, to sharpen the focus on areas of disagreement, to suggest in specific instances the terms on which a compromise might be possible. Call it what you will - full brokerage, honest partnership, instant shuttle - that's how read the president's approach, and it strikes us as eminently sensible.