Ariel Sharon has proposed a new "disengagement plan" in his recent speech at a conference in Herzliya. The plan calls for Israeli forces to withdraw unilaterally from the West Bank, behind a perimeter marked by the "security fence" currently under construction. (The fence mostly follows the 1948 Israeli-Jordanian border, but juts out in places well into the West Bank.) The plan also calls for some settlement outposts beyond this perimeter to be dismantled.

The plan has drawn mixed reviews. about 60% of Israelis support it, but many on the left doubt that it will actually be implemented. Meanwhile, the right complains that it represents a victory for terrorists, and a defeat for settlers.

I have a more mundane objection to the plan: it's doomed to fail. The standard argument for withdrawing behind a security fence is that it has succeeded in Gaza, since no suicide bombers have launched attacks on Israel from there. But it's also the case that from Gaza--where the IDF never launched a full-fledged invasion of all the cities, as it did in the West Bank--there has been a steady rain of crude rockets on adjacent Israeli lands, such as the Gaza settlements and the town of Sderot (inside pre-1967 Israel). If the IDF were to "disengage" from the West Bank, it might well be able to prevent suicide bombers from penetrating its security perimiter. But it would be incapable of preventing massive barrages of rockets on towns near the perimiter--including several major Israeli cities.

What would Israel do in such a situation? if it returned to the West Bank in force, it would be no better off than it is now--indeed, worse off, since it had afforded the terrorist organizations time and space to regroup and rejuvenate themselves. If it restrained itself from re-entering the West Bank, it would have to respond from a distance, using weapons, such as artillery and helicopters, that are much more likely to cause collateral civilian damage, and thus earn condemnation from world opinion. And it would run the risk of international "observers" or "peacekeepers" entering the territories in Israel's absence, and turning into de facto defenders of the terrorists' turf.

The security fence is clearly a necessary measure for the protection of Israelis. And the Israeli far right's complaints notwithstanding, there's nothing wrong with the removal of a few settlement outposts, if it improves Israel's security situation. But abandoning the West Bank to the mercy of Arafat's goons, Hamas, Islamic Jihad and the rest is good neither for its inhabitants nor for their Israeli neighbors. Israeli politicians should stop treating this option as if it were a remotely viable one.