The administration has spent months trying to avoid casting its veto in the Security Council to block membership of a Palestinian state. It also hopes to avert a vote for the more symbolic change in status in the General Assembly, which senior officials, echoing the Israelis, have warned would be harmful to Israeli-Palestinian peace and could foment violence.

But with negotiations long stalled, the Palestinians and their allies say that such a vote would preserve the idea of a two-state solution.

The timing of the confrontation has created a diplomatic quandary for President Obama, putting him in the position of opposing Palestinian aspirations for self-determination even as his administration has championed Arabs who have overthrown leaders in Egypt, Tunisia and Libya or who seek to in Syria. At the same time, he faces pressure from Israel’s vocal supporters in Congress to block the vote or cut off military and economic assistance the United States has given to the Palestinians.

Internationally, however, the United States and Israel appeared increasingly isolated, with even some European nations, from Russia to France, signaling support for at least a General Assembly vote for the Palestinians.

The support for the Palestinians from the Turkish prime minister was not a surprise, but the commanding tone of his endorsement — coupled with Turkey’s souring relations with Israel, once a close ally — underscored the growing sympathy for Palestinian aspirations for sovereignty and statehood.

“Let’s raise the Palestinian flag, and let that flag be the symbol of peace and justice in the Middle East,” said Mr. Erdogan, the increasingly influential leader of a NATO ally. He also took a harsh tone toward Israel, saying it is “the West’s spoiled child.”

The Arab League signaled that it would press the Palestinians to seek a General Assembly vote to elevate the status of the Palestinian Authority from nonvoting “observer entity” to “observer state.” Some Palestinian leaders, though, continued to press for a Security Council vote.