AMMAN, Jordan -- Vice President Joseph R. Biden, winding up a disconcerting trip to the Middle East, struggled Thursday to keep hopes alive for new peace talks amid intensifying Palestinian anger over Israeli plans for new housing construction in a disputed Jerusalem neighborhood.

Despite earlier pledges to take part in talks scheduled to begin next week, Palestinians officials threatened to stay away unless Israel abandons its announced plans for a 1,600-unit project in disputed East Jerusalem.

Palestinians pressed for the United States to change Israel's stance on the project. While U.S. officials voiced unhappiness with Israel, they also praised a government apology that voiced regret over the timing of the announcement but did not cancel the plan.

Senior Palestinian negotiator Saeb Erekat said on Voice of Palestine radio that Palestinian President Mahmoud Abbas would not take part in talks unless Israel drops the project. In interviews, other Palestinian officials concurred with Mr. Erekat's view.

But Mr. Erekat was quoted by other news organizations later Thursday as saying Mr. Abbas was not setting conditions for Palestinian participation, although he hoped that the United States would persuade the Israelis to halt the building project.

The sharp shifts in positions came as Mr. Biden worked to lobby leaders of both sides in a bid to rescue the talks. He held a midday phone call with Mr. Abbas and also spoke with Israeli Prime Minister Benjamin Netanyahu. U.S. officials said they expect the Palestinians to take part.

Nonetheless, the uncertainty suggests that the peace effort lost ground this week, as Mr. Biden visited Israel on a mission to mobilize both sides to begin talks after a yearlong interruption.

His trip was disrupted by the Israeli announcement Tuesday that it intended to build the new housing for religious Israelis in a subdivision called Ramat Schlomo. Mr. Biden, embarrassed and angered by the announcement, criticized Israelis in unusually strong language for two consecutive days, as he met first with Israeli leaders, then with Palestinian counterparts.

The incident seemed to further shake already weak Palestinian support for the new talks. And Israelis have shown little enthusiasm for a return to indirect talks, which would be mediated by the United States, after a year without face-to-face negotiations.

In a speech at Tel Aviv University, Mr. Biden called on both sides to continue peace efforts, saying "the status quo is unsustainable."

Mr. Biden hailed a statement by Mr. Netanyahu suggesting that the Ramat Schlomo project would take so long that the issue might be rendered moot by completion of negotiations over control of Jerusalem. Mr. Netanyahu said remaining approvals for the project "will, in all likelihood, take more than a year, and the beginning of actual construction would likely take several years."

But Israel's position is that construction in Jerusalem is legal and proper, and Mr. Netanyahu didn't imply that he disapproved of the construction.

The Israeli leader instructed other government officials to avoid disruptive announcements of construction projects like the one unveiled Tuesday.

Mr. Biden flew Thursday afternoon to Amman, Jordan, to consult with Jordan's King Abdullah on peace talks and other issues before he returns to Washington today.

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