Since December 2003, Ariel Sharon has astonished friend and foe alike, embracing the very idea he opposed in the elections that confirmed him in power in January 2003.

The idea is "unilateral disengagement," whereby Israel, without a peace agreement, withdraws its military and civilians from the territories administered by Israel since the 1967 war -- in this case, the Gaza Strip. The Labor opposition's Amram Mitzna lost badly campaigning on this very platform, coming in for incisive criticism from not a few figures, not just among the governing Likud, but from a bevy of informed Israeli observers. To cite just two:

Historian Michael Oren: "The minute you pull out of Gaza you signal to the Arabs that you're in retreat. It's a huge victory for the Palestinians. Palestinians will have huge celebrations in Gaza. You think they'll sit down and talk after that?"

Respected centrist journalist, Yossi Klein Halevi: "If unilateral withdrawal could happen in a void, it would be the right decision But it is not happening in a void . . . The psychological implications are to reinforce the post-Lebanon withdrawal perception in the Arab world that we are a defeatist society and with enough pressure we'll simply withdraw."

Indeed, Ariel Sharon himself could not have been clearer at the time: "A unilateral withdrawal is not a recipe for peace. It is a recipe for war."

If these criticisms are correct, then unilaterally withdrawing from Gaza is a victory for terrorism; bloodshed is likely to flow from it, and Sharon of all people must know it.

What, then, is Sharon's rationale? According to his supporters, both right and left, the withdrawal represents Israel seizing the initiative, setting its own lines of defense, and preempting noxious diplomatic initiatives from Israel's ill-wishers. But all this looks doubtful. True, the Israel Defense Forces will be relieved of the onerous duty of defending isolated Jewish communities in a sea of enemies, but its absence from Gaza will also afford Palestinian terrorist groups a freer hand for mounting further attacks. And an initiative that stimulates the aggression of terrorists will not be altered by its originating in Jerusalem, as the terrorists themselves make clear.

Thus, Sami Abu Zuhri, a Hamas spokesman, has opined, "all the Israeli statements about a withdrawal from Gaza Strip are due to the Palestinian resistance operations. We are completely confident that as the Hezbollah Organization managed to kick the Israeli forces out of Lebanon, the Palestinian resistance will kick them out of the Palestinian territories, and we will continue our resistance."

A top Hamas leader in Gaza, Mahmoud al-Zahar, concurs: "Very simply, nobody can deny that if Israel is going to leave the Gaza Strip and part of the West Bank, that was because of the intifadah, because of the armed struggle, because of the big sacrifices of Hamas for this goal."

Add to this that the current cease-fire is giving terrorists a breather from ducking into bunkers and dodging Israeli drones, all the while recouping for another round.

All indications, then, are that the terrorists will be the leading beneficiaries of a unilateral Israeli withdrawal, appearing vindicated in asserting that terrorism first and foremost is the way. When the cease-fire collapses, as it must, foreign offices the world over will be clamoring for still more diplomatic motion and will take a dim view of resumed Israeli counter-terrorism measures. If setting the agenda, securing one's own, and preempting dangerous diplomacy is the idea behind the Gaza withdrawal, Israelis are likely to be disappointed.

Indeed, it could be said that Sharon is pursuing this doomed initiative as a result of diplomatic defeat. The "road map" peace plan was always going to serve as a guarantor of Palestinian malfeasance. Devised by the European Union, United Nations, the Russians, and the US State Department, the road map is to lead to a Palestinian state regardless of what Palestinians do.

Ingenious explanations can be offered for Israel's actions, but only one fits all the facts -- the Israelis are punting, grasping for a solution that is all the more enticing for looking like what in other circumstances might be sound policy. Instead, it has the savor of panic and defeat, made worse by delusive rationalization.

The Israelis are in the unpleasant position of making do with policies they opposed at the ballot box. But the United States is in no such position. Americans are fighting the same Islamist terrorist groups. The Bush administration, which looks like it's rewarding the unreconstructed Palestinian Authority with levels of aid not even contemplated by Bill Clinton in his more expansive moments, should think twice about supporting policies that weaken its best Middle Eastern ally while emboldening the terrorists it is also fighting. It is not too late for a dose of good sense.

Daniel Mandel is associate director of the Middle East Forum in Philadelphia and author of "H.V. Evatt and the Establishment of Israel: The Undercover Zionist."