PEACE IS a winner," Secretary of State Shultz insists, and we think he is right. But peace sure isn't a quick and easy winner. To the Begin government's harsh rejection of the new American peach plan has now been added a soft rejection by the 20 Arab governments that assembled with the PLO at Fez.

Ignoring the American call for negotiating with Israel a West Bank territorial compromise and a self-governing entity "in association with Jordan," the Arabs at Fez simply demanded creation of a PLO state in all the territory lost in 1967. Their plan says not a word about negotiating with or recognizing Israel -- legitimate Israeli demands. "Peace among all states of the region" (in that phrase lies the plan's only evident reference to Israel) would be guaranteed by -- don't laugh -- the U.N. Security Council.

American officials had hoped that at Fez the Arabs would start easing off their eight-year insistence that the PLO alone speaks for the Palestinians. But Fez reaffirmed the earlier Rabat endowment of a PLO political monopoly. Its practical meaning is to freeze Jordan out of any dealing for West Bank Palestinians, and thus to flout the key American strategy of drawing Jordan in.

The earlier Fahd peace plan called for Arabs to accept "the right of states of the region to live in peace." This was too little for Israel but too much for Arab radicals, who shot the plan down. This time the radicals joined the drafting party: the new Fez plan relieves Arabs of any obligation to accept even the modest offering of King Fahd. Instead, Fez suggests that the Security Council "guarantee peace among all states of the region, including the independent Palestinian state." Why the toughening at Fez? The difference apparently was the Lebanon war, which enabled the PLO to play on the guilt and vulnerability felt by the Arab states for having abandoned the PLO in Beirut.

So Fez was a triumpt for the PLO, but a triumph achieved at a price. The Arabs have a show of unity around a potition that Israel rejects and the United States cannot support. If they stick to the Fez plan, they will have kicked away the tremendous offer Mr. Reagan has made to help them achieve an imperfect but worthy goal.

Will they stick to Fez? Certainly Menachem Begin, for one, must hope so. The Fez plan ensures that the American proposals will not get off the ground. It bars an approach to the table by the one negotiating partner, Jordan, specified by the United States and suitable to Israel. It enables Israel to escape the onus of being the sole spoiler. The Begin government went into Lebanon believing that the operation would let it solve the Palestinian problem in its own restrictive, unacceptable way. The Arabs at Fez seemed intent on proving Mr. Begin right.

The United States, however, can no more take Fez as the last Arab word than it can take the Begin government's potition as the last Israeli word. Mr. Shultz probably went too far in suggesting that there could be value in the Fez plan if it turns out (it's not clear from the text) that it implies Arab willingness to recognize Israel; the Egyptian-Israeli example once and for all devalued such formulas of evasion as "implied recognition" and "non-belligerency" and established face-to-face talks and full normalization of relations as the sine qua non of peach in the Middle East.

Mr. Shultz was unquestionably right, however, to emphasize a continued American search for an Arab negotiating partner. The article in Topic A today by Labor Party Leader Shimon Peres suggests that there may yet be an Israeli negotiating partner as well. The American proposals remain fair, necessary to pursue and, we believe, ultimately achievable. A week ago, we suggested that the Israelis were testing Mr. Reagan. So are the Arabs. The going will be rough.