Part of the problem in bringing about a peace settlement in the Middle East has been the inability of the Arab states to unite their policy and present a cohesive front. So it is not insignificant that at the recent Arab gathering in Fez, Morocco - the first such meeting after President Reagan's Mideast initiative - 20 Arab League members met and for the first time agreed on their own peace plan. At least this is an effort to move forward.
Last year, it will be recalled, a similar meeting in Fez ended in humiliating disarray. Saudi Arabia could not deliver US support for its peace plan, Syria decided at the last moment to stay away, and the conference collapsed. This time the Arab moderates and Arab ''confrontationists'' at least got together and agreed on a joint approach - an outcome no doubt spurred by the Reagan administration's indication that it is prepared to engage itself seriously in the peace process.
Substantively, the joint plan seems to be basically a reworking of the eight-point Saudi plan. It clearly is unacceptable to Israel. It also departs from the proposals put forth by the United States, calling as it does for the establishment of a Palestinian state in the West Bank with East Jerusalem as its capital and the dismantling of existing Jewish settlements. One of course could not have expected the Arabs to embrace the Reagan plan as their initial position. But it does seem that a more forthcoming response would have had a better chance of persuading moderate opinion in Israel that the Arabs truly want an accommodation. The domestic political pressures on Mr. Begin might have been heightened.
Yet the Arab plan contains some positive elements. Most important, it gives implicit recognition to Israel by leaving to the United Nations Security Council the task of guaranteeing the security of ''states in the region'' - a proposal favored by the Tunisians. Acceptance of this formulation by all shades of Arab opinion on an issue of such basic concern to Israel can be viewed as encouraging.
Bridging the difference between Israel's peremptory rejection of the Reagan initiative and the Arabs' counterpoint will be a big challenge, to put it mildly. But the President appears to be achieving his early objective - to unscramble the Mideast diplomatic stalemate, stir reactions, and build public momentum for a renewed peace negotiation. In this context, the Fez summit meeting can be counted a success for US diplomacy.