As Israeli politicians visiting the United States generally do in the months before an upcoming Israeli election, Prime Minister Ariel Sharon spent part of his visit to New York last week lining up financial backers in the American Jewish community for his next campaign. There is as always something embarrassing about this, let alone questionable in terms of Israeli electoral law. There isn’t another country in the world whose political parties depend on contributions from abroad, and it would be hard to argue that this is a healthy phenomenon.

In the present case, moreover, Ariel Sharon’s potential backers don’t even know what party in Israel they are being asked to back. Is it the Likud, at the head of which the prime minister will remain if he can win the battle for control of it that he is now conducting with Benjamin Netanyahu? Is it the new centrist party that he is said to be considering founding, should he lose to Mr. Netanyahu, by leading a breakaway faction out of the Likud that would merge with a similar group from the Labor Party and other elements – the so-called “big bang,” in current Israeli parlance, that would totally explode the political map of Israel? Or is it only a “small-bang” party consisting of those bolting from the Likud alone?

Mr. Sharon himself, it would seem, does not yet know the answer to these questions. Perhaps he will know it better after next week’s vote in the Likud’s Central Committee over whether to hold early primaries for electing the party’s leadership for the scheduled 2006 national elections – a step that the prime minister and his supporters, who fear a Netanyahu victory, are resisting. If Mr. Sharon loses the Central Committee vote, speculation has it, he will leave the Likud for either the “big bang” or “small bang” alternative. His financial backers in New York should think carefully before encouraging him to do this. It isn’t necessarily a good idea.

In the first place, it would be a premature concession of defeat on the prime minister’s part. He is currently, in the wake of the Gaza disengagement, more popular with Likud voters at large than he is in the party’s institutions, and a loss to Mr. Netanyahu in the Central Committee need not mean a loss in early primaries. These could still be won by him, leaving him at the head of Israel’s largest and best-organized political force, which would certainly be the best springboard for him to seek re-election from. At the very least, it would make sense for him to contest the primaries first and only found a new party if he lost them.

But even if Mr. Sharon did lose the primaries, running at the head of a new center party, composed of disgruntled defectors from the Right and the Left and appealing to a similarly disgruntled public, is an idea that should give him pause. The precedents in Israeli political history have not been encouraging.

Yes, the polls show the prime minister running strongly on such a list, garnering 38 seats in the 120-member Knesset in a “big-bang” scenario and slightly less in a “little-bang” scenario, and in either case heading the largest parliamentary bloc. Yet the Israeli experience shows that new parties tend often to do well in early polls and then slump at election time as they lose their fresh glamour and suffer from amateurish organization and the last minute tendency of voters to revert to old loyalties. In 1999, for example, a new Center Party led by a quartet of political stars, three of them prominent Likud dropouts, ended up with six Knesset seats after having 20 predicted by early polls. Something similar could happen to Ariel Sharon.

Yet even if it doesn’t, and he indeed emerges from new elections with the largest parliamentary bloc and puts together a coalition government led by himself, this government is unlikely to accomplish a great deal. Since it will be an amalgam of personalities and forces with differing viewpoints on all major social and economic issues except the need for further disengagements like the Gaza one, it will in effect be a single-issue party, and yet, paradoxically, this single issue will be the one that it will be most unable to advance.

The reason is simple. From Menachem Begin’s withdrawal from Sinai in 1979-82, as part of the Israeli-Palestinian peace treaty, to the disengagement from Gaza this summer, Israel has been politically able to make significant territorial concessions only when the Likud, or a significant part of it, is part of the process. When it isn’t, as was the case with the Oslo Agreement signed by the Labor Party in 1993, the consequence is civil strife too severe to allow forward movement to take place.

A Sharon government with the Likud in opposition will be a government that will find more unilateral disengagements in the future all but impossible to carry out. And meanwhile it will have inflicted major damage on Israel’s shaky political structure, which has too many parties in the Knesset already, by severely weakening both Labor and the Likud through the introduction of a new parliamentary grouping which will itself almost certainly fly apart or shrink drastically in the end. This at least has been the fate of every initially successful new center party in Israel until now, starting with the renowned archeologist Yigael Yadin’s Democratic Movement For Change in 1977,and there is no reason to suppose that yet another will prove more cohesive in the long run.

If Ariel Sharon does end up losing the leadership of the Likud to Benjamin Netanyahu, he and his supporters might do Israel the greater service by remaining in the party and fighting for their beliefs from within. The encouragement he would need to make such a decision, however, is not of the financial kind.

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