Call it a triumph of hope over experience.

When Israel agreed to a 10-month partial settlement freeze last year, U.S. officials said it was exactly what they needed to get talks with the Palestinians started. They whispered that they were sure the freeze would be extended; Israel wouldn't dare curtail the negotiations by ending it.

When the talks finally started in September - after the Palestinians balked at direct negotiations for nine months - U.S. officials again asserted that the sheer momentum of the talks would carry them past the end of the moratorium later that month. Yet the moratorium ended, and the talks flagged.

Now, U.S. officials are taking another leap of faith - on a 90-day settlement freeze.

The theory is that if the sides can establish the borders of a Palestinian state, and it is clear which settlements will become part of Israel and which will be dismantled, the issue of settlement expansion will fade in importance and the talks will keep going.

This appears to be the last chance. Under a tentative agreement struck between Israeli Prime Minister Binyamin Netanyahu and Secretary of State Hillary Rodham Clinton, the Obama administration agreed never again to ask for a settlement freeze. The administration also agreed to exempt the area surrounding Jerusalem from the freeze.

On top of that, the Obama team agreed to veto anti-Israel resolutions at the United Nations and to sell $3 billion worth of fighter jets - essentially, a payment of $33.3 million for each day of the freeze.

At this point, Netanyahu appears to be on track to win narrow approval of the plan; Palestinians have withheld judgment, but initial reactions have been skeptical. But even if the new freeze is implemented, virtually no analyst believes an agreement on borders is possible in 90 days.

Daniel Levy, a former Israeli peace negotiator and now a senior research fellow at the New America Foundation, said there is "not a hope whatsoever" that the two sides can agree on a border within 90 days if left to their own devices. He said that the only way to make real progress is for the Obama administration to offer its own formula for the border, thus forcing a "yes or no" moment for the Israeli government.

"Ninety days seems pretty short," said Nathan J. Diament of the Union of Orthodox Jewish Congregations of America. The compromises will be very difficult, he said, and there is little trust or confidence between the two sides. "Negotiations don't have a self-sustaining momentum, no matter how determined George Mitchell is," he said, referring to President Obama's peace envoy.

Part of the problem is that Israel's main bargaining chip is land, and it would be required now to give up land without knowing precisely what it would get in return. Palestinians have been willing to consider swaps, getting land in exchange for giving up settlements on claimed Palestinian territory, but have insisted on 100 percent of the total square miles held before the 1967 Six-Day War.

In 2008, then-Prime Minister Ehud Olmert offered 99.3 percent when he negotiated with the Palestinians - he wanted credit for a land corridor between the Gaza Strip and the West Bank - and it is doubtful that the more conservative Netanyahu would give up even more.

"The question is whether Netanyahu and his coalition . . . are willing to sign an agreement that will effectively return Israel to the 1967 borders," Israeli political commentator Nahum Barnea wrote Monday in Israel's mass-circulation daily Yedioth Ahronoth. "Are they willing to do this even before the question of the right of return and the question of Jerusalem have been discussed? If so, we can tip our hats to them. They are brave people, who are not reluctant to change their opinion completely, people who have seen the light. Otherwise, they are risking a bitter quarrel with the U.S. administration. They are selling our birthright for a mess of pottage."

The "right of return" is the Palestinian's main trump card - giving up their right to return to homes in Israel. Deferring the issue of Jerusalem, which Palestinians also want to claim as their capital, until after the 90-day period is also problematic, analysts said. Striking a deal on borders without tackling Jerusalem would mean that Israeli building in areas now claimed by Palestinians, such as East Jerusalem, would continue to be a source of tension.

"How can you negotiate a border agreement without negotiating Jerusalem?" asked Elliott Abrams, deputy national security adviser in the George W. Bush administration who is now at the Council on Foreign Relations. Jerusalem, whose Old City is claimed as holy by Jews, Muslims and Christians, is perhaps the most difficult "final status" to overcome, with key members of Netanyahu's coalition insisting that not an inch will ever be given up.