Talks on forming a united Palestinian Authority government between West Bank-based Fatah and Gaza-based Hamas commenced in Cairo last week. Egypt is sponsoring the talks, with the tacit blessings of the international community.

This is a mistake. The Obama administration should take a close look at the likely consequences of such an arrangement.

Hamas enters these talks from a position of relative popularity in the West Bank following the recent Gaza war, whereas the Fatah leadership continues to be weak - its institutions have not been reformed since its election loss to Hamas in early 2006.

This means the new Palestinian elections that a unity government would be duty-bound to hold in the West Bank and Gaza within months of its formation could produce a Hamas president of the PA to replace Fatah's Mahmoud Abbas, and another Hamas-dominated Palestinian parliament to replace the current one that was elected because the Bush administration insisted Hamas be allowed to run three years ago.

Hamas won those elections fair and square, but the parliament never really functioned due first to Israel's arrest of Hamas legislators, and then to the collapse of an earlier Hamas-Fatah unity government in June 2007, when Hamas took over Gaza by force.

Hamas's status among Palestinians has been aggrandized by both American and Israeli mistakes. Allowing the 2006 elections was one. Refusing to accept the results was another. Besieging Hamas in Gaza - refusing to engage it and boycotting 1.5 million Gazans economically unless Hamas recognized Israel and renounced violence - seems to have strengthened the movement, as did the recent war, an abortive attempt to apply a military solution.

A Hamas-Fatah unity government throughout the West Bank and Gaza would hardly constitute an improvement. The leading Palestinian political pollster, Khalil Shikaki, argues that right-wing tendencies have grown and reinforced one another in both Israel and Palestine since the failure of the Camp David summit in 2000.

In Palestine, the Islamists (Hamas) are replacing the nationalists (Fatah). The ramifications of the Gaza war point to an additional shift to the Islamists if Palestinian elections were held. Against this backdrop, Fatah may feel it has no alternative but to share power with Hamas.

Egypt and the international community may conclude that the only way to enable reconstruction aid to enter Gaza is for a unity government to deploy Fatah-oriented PA forces at the Gaza crossings. That way the aid would arrive without Hamas personnel actually handing it to needy Palestinians.

This would be a dangerous exercise in self-deception. Even before any new Palestinian elections, a unity government would probably mean accepting dramatic changes in the Palestinian security services to reflect Hamas's influence.

This would effectively end the Dayton mission that trains and deploys a new generation of Fatah-oriented security forces that confront West Bank Hamas and have been restoring law and order. The training is one of the few demonstrably positive developments the Bush administration and the outgoing Olmert government can point to in the Palestinian sphere.

A regression in the West Bank security situation, whether triggered by a unity government or a consequent Hamas victory in new elections, would be unacceptable to the government of Israel, whoever is in it. Nor would an Israeli-Palestinian peace process be as easy to manage with Hamas in the PA government. Jordan, too, would not like to see Hamas, which is the Palestinian branch of the Muslim Brotherhood, on its western border.

All this would mean a huge setback for the Obama administration's hopes to begin putting the Israel-Arab conflict on the right track.

The solution does not lie in acquiescing in a Palestinian unity government. American and other policy planners who encourage a unity government in the (correct) belief that ultimately Palestinian unity is a necessary precursor to a comprehensive two-state solution, will end up with no solution.

Of course Bush-era U.S. policy toward the Israeli-Palestinian conflict has to be rethought and revised by the Obama team. But a unity government should be the final phase before a two-state solution, if indeed one is still possible, not the initial phase.

Instead, now is the time to begin dealing differently with Hamas. Talk to it, yes. It's a terrorist organization, but it controls finite territory on Israel's borders, hence it must be engaged, like Iran and Syria, without conditions. Forty percent of Israelis already favor such a step.

Stop starving Gazans. Deliver the aid directly to Hamas with adequate international controls to ensure it is not used to build fortifications. At the same time, quarantine Hamas politically and keep it out of the West Bank - a far more strategic piece of land than Gaza - until and unless it radically moderates its world view.

Yossi Alpher, former director of the Jaffee Center for Strategic Studies at Tel Aviv University, coedits the bitterlemons.org.