WASHINGTON — President Obama, seeking to capture a moment of epochal change in the Arab world, began a new effort on Thursday to break the stalemate in the Israeli-Palestinian conflict, setting out a new starting point for negotiations on the region’s most intractable problem.

A day before the arrival in Washington of Prime Minister Benjamin Netanyahu of Israel, Mr. Obama declared that the prevailing borders before the 1967 Arab-Israeli war — adjusted to some degree to account for Israeli settlements in the West Bank — should be the basis of a deal. While the 1967 borders have long been viewed as the foundation for a peace agreement, Mr. Obama’s formula of land swaps to compensate for disputed territory created a new benchmark for a diplomatic solution.

Mr. Obama’s statement represented a subtle, but significant shift, in American policy. And it thrust him back into the region’s most nettlesome dispute at a time when conditions would seem to make reaching a deal especially difficult.

The Israeli government immediately protested, saying that for Israel to return to its pre-1967 borders would leave it “indefensible.” Mr. Netanyahu held an angry phone conversation with Secretary of State Hillary Rodham Clinton on Thursday before the speech, officials said, in which he demanded that the president’s reference to 1967 borders be cut.