In recent weeks, Mr. Kerry and his aides have outlined several basic arguments for why his efforts might bear fruit. Perhaps the most important one, which Mr. Kerry advanced almost the moment he was picked for the State Department post, is that the United States does not have the luxury of staying on the sidelines.

With the Palestinians poised to take their claim for statehood to the International Criminal Court and United Nations bodies, American officials say the two sides were facing a downward spiral in which the Israelis would respond by cutting off financing to the Palestinian territories and European nations might curtail their investment in Israel, further isolating the Israelis.