At CAMP DAVID, Israel and Egypt accepted "a goal of concluding within three months" a peace treaty. The inevitable political buildup plus verbal carelessness made it, in Jimmy Carter's word, a "deadline," and it came and went yesterday with no agreement and general dismay. It is a serious lapse, at the least calling into question the two parties' political capacity to honor the solemn commitments the took on at Camp David. Mr. Sadat, under Arab pressures, made demands that Mr. Begin, under domestic pressures, refused. Yet the lapse need not be fatal, if its particular cause is understood.

The cause does not lie in the basic intractability of the Mideast problem or in the bad faith of any one party. It arises from the requirements Camp David places on American diplomacy to be an honest broker. If Washington takes sides, it risks forcing a stallout. This is what happened last week.

Secretary of State Vance spent most of the first three days in Cairo working on what turned out to be not an Egyptian position to take Israel to negotiate but an Egyptian-American position to take Israel to impose. As President Carter put it on Thursday, the day Mr. Vance moved to Jerusalem, "The proposition that has been worked out with Egypt is presented clearly to the Israelis . . . to either accept it or reject it." When, predictably, the Israelis did the latter, Mr. Carter let it be known that he was "livid" and "frustrated." There was more.

Would Israel have negotiated the Egyptian position if it had not come in the form of an American dictate and if it had not been presented (by an administration impatient, it says, with the parties' resort to the media) with public pressure? All Israelis are extraordinarily wary of the Camp David process and some would eagerly seize on a pretext to retreat - especially from the commitment to negotiate "full autonomy" for Palestinians. But that is precisely why the administration must heed its style. Otherwise it defeats its own stated purpose of mediation.

The prime difference in text between Egypt and Israel is "linkage" - whether the key symbolic act of exchanging ambassadors, which is due to take place after Isrealhs agreement to Palestinian self-rule. A second difference is "priority of obligations"-whether Egypt's new obligations to Israel to make peace override its old obligations to fellow Arabs, in certain circumstances, to make war. We cannot believe that the words with which these differences might be composed, in so far as words rather than events can compose them, are beyond Egyptian and Israeli wit. Israelis has already tentatively approved some of the very words they now contest before the waters were muddied.

Last week Egypt over-asked, the United States overpushed, Israel over-reacted. But there is this week, and subsequent weeks if they are needed-though Israel and Egypt should know that the United States and Mr. Carter have other heavy business on their international plate. The balance between the three actors must be recalibrated and each to them must realize how its style as well as its substantive policy plays into the style and policy of the others.