PROGRESS IS finally being made in the matter of Israel's long overdue withdrawal from Lebanon. The Israelis had demanded security guarantees -- negotiated ones from Lebanon, tacit ones from Syria -- to cover the departure of the 12,000 or so troops left from its 1982 invasion. So far, the Lebanese, dominated by Damascus, have been unable to offer such guarantees, and the Syrians, playing a larger game, have been unwilling to. As a result, Israel, pained by the continuing casualties and economic and diplomatic costs, has now decided to withdraw on its own. Its plan reflects the priorities of Prime Minister Shimon Peres, whose Labor Party seeks to extract the country from the quagmire his Likud coalition partners got into in Lebanon while they were governing alone.

The three-stage Israeli plan anticipates a unilateral withdrawal from part of the coastal region within the next five weeks, then from the Bekaa Valley and then, "six to nine months" from now, the rest of the way to the international border. Ready or not, the Israelis say, we're leaving. By stating the plan in this form, the Israelis intend to jolt the Lebanese and others into joining to make cooperative arrangements for the control and security of the areas being evacuated, lest Israel be left free to make its own arrangements with local militias or lest chaos follow instead.

Along the southern strip of Lebanon, the Israelis want in the end to maintain control through a client militia and their own regular patrols. This is a clear challenge to Lebanese sovereignty. The Lebanese government's best response is to demonstrate, against the difficult odds, that its army can do a serviceable security job. Its antagonists here include not only the Druze and Christian units supported by Israel but also the Shiite Mosems who have bedeviled Israel's occupation of southern Lebanon. The United Nations forces on the scene will be essential, although their number and deployment are subject to a great-power consensus, and Moscow is currently using its leverage to work itself into a larger U.S.-acknowledged Mideast role.

"After two-and-a-half years in Lebanon we have learned the hard way that Israel should not become the policeman of Lebanon," says Israel's defense minister, Yitzhak Rabin. Lebanon, too, has learned the hard way that Israel should not become the policeman of Lebanon. The PLO as an organized and oppressive force in Lebanon was ousted by the Israeli invasion, but Lebanon paid a very high cost in terms of life, property and viability as a state. Still, it's good that Israel is withdrawing. What about Syria?