As has been widely pointed out this week in Israel, although the disengagement from Gaza is officially scheduled to begin in the second half of August, it is in effect already under way. The intensification of pro-settler protests; the first violent skirmishes between the army and groups of anti-disengagement militants in Gush Katif, the southwest corner of the Gaza Strip in which most of the settlements are located; and the 18-to-3 vote in Sunday’s cabinet session in Jerusalem to reject a last-ditch, settler-supported proposal to postpone the rapidly approaching withdrawal by several months – all are part of Phase 1 of disengagement itself.

Disengagement from Gaza will take place. And yet its ultimate success depends not only on Jerusalem and the determination of Ariel Sharon, but also on Washington and the wisdom of George W. Bush and Condoleezza Rice. There are worrisome signs that, when it comes to the Israeli-Palestinian conflict, President Bush and his secretary of state may not turn out to be less wise than one had assumed.

These signs consist of recent U.S. declarations, most but not all coming from the State Department, criticizing Israel, on the one hand, for continued “settlement activity,” even in those areas near the 1967 Israeli-Jordanian armistice lines with large Jewish concentrations that have been publicly acknowledged by the president to be unsurrenderable; and reiterating, on the other hand, the traditional U.S. position that any changes in the 1967 lines have to be mutually agreed upon in Israeli-Palestinian peace negotiations.

It is possible, of course, that all this is merely lip service to what both the White House and the State Department consider unavoidable public commitments. The “inadmissibility of acquiring territories by force” and the need for, and possibility of, a negotiated peace treaty between Israel and an independent Palestinian state have always been the official cornerstones of American policy, as they are of the Bush “road map.” It would be surprising if they were to be openly abandoned even if, privately, they are conceded to be inoperable.

Let us hope so that such a private realization exists. The fact is that a negotiated peace treaty between Israel and a Palestinian state, or at least a treaty that can last, is simply not in the realm of possibility. Any U.S. policy based on the illusion that it is will doom the region to many more years of conflict and frustration.

Indeed, the assumption that a formal Israeli-Palestinian peace treaty is not achievable is the entire logic behind Ariel Sharon’s disengagement plan.

This plan is predicated on the belief, firstly, that in the absence of such a treaty Israel must act on its own to demarcate its permanent borders; secondly, that these borders must strive to be both militarily and demographically optimal, that is, to include within them as many strategic assets and Jewish settlements as possible while freeing a maximum of Palestinians from Israeli domination; and, thirdly, that an Israel existing within such borders, even if unacceptable to the Palestinians in principle, stands a reasonable chance of being tolerated by them if it is backed by Israeli military might, a relatively unified Israeli society, and – the support of the United States.

This support is crucial. If it does not come from America, it will certainly not come from Europe; and in its absence, the Palestinians, with the encouragement of the Arab and Islamic worlds, will not only refuse to recognize Israel’s new borders but will continue to oppose them by violence.

In actual fact, it will not even come to that. Unless the United States makes it clear that unilaterally determined borders that annex only the minimal areas Israel must have will be recognized by it as legitimate, it is politically inconceivable that the painful disengagement from Gaza can be followed by the even more painful disengagement from most of the West Bank that Ariel Sharon has in mind. There is no way that Mr. Sharon or any other Israeli politician can obtain public approval for a major West Bank withdrawal unless Israelis feel confident that America will stand behind the frontiers created by it.

What will happen if such approval is unobtainable? The disengagement that started with Gaza will end with Gaza, and the West Bank will continue to be violently disputed territory, with Palestinian militants, the Israeli army, and Jewish settlers all involved in endless and worsening spirals of warfare. And what will not happen is a peaceful resolution of this warfare, if only because increasing radicalization in both societies, as illustrated by the growing strength of Hamas in Palestinian life and of the settlement movement in Israel, will make common ground more and more impossible to find. That which could not be achieved in the year 2000 between Ehud Barak and Yasser Arafat will not be achievable in 2010 or 2020.

To continue to insist on a comprehensive Israel-Palestinian peace treaty is therefore to continue to insist on never-ending Israeli-Palestinian territorial conflict. The only way to end this conflict is for Israel to disengage from it, which cannot be done without at least tacit American backing. This does not mean that George W. Bush and Condoleezza Rice must officially announce that the “road map” is dead, and with it all hope for a negotiated peace. But it does mean that they must come to terms with the fact that this is so and make a clear distinction in their own minds between practical policies and impractical if necessary rhetoric. Otherwise, such rhetoric will lead to more disaster.

Mr. Halkin is a contributing editor of The New York Sun.