The Obama administration is trying to cajole the Israeli government into a 60-day renewal of the freeze on Jewish settlement building by offering it security guarantees, ranging from military hardware to support for a long-term Israeli presence in the strategically sensitive Jordan Valley, according to lawmakers and other officials briefed on the proposals.

But with Prime Minister Benjamin Netanyahu so far resisting the administration’s entreaties, the United States is also weighing a fallback plan, officials said, that could involve reaching out to the Palestinians with a pledge to formally endorse one of their central demands for the borders of a future Palestinian state.

The American proposals to Israel came amid a frenzy of diplomatic horse-trading, with the administration maneuvering furiously to keep the talks alive while Mr. Netanyahu appeared to be trying to extract a high price for acquiescing on settlements. The Palestinians have threatened to walk away from the talks if Israel does not renew its freeze on construction, something Mr. Netanyahu has ruled out.

Adding to the pressure is a meeting in Cairo next week of the Arab League, at which the Palestinian Authority president, Mahmoud Abbas, has promised to deliver a speech in which he will “declare historical decisions.” That sparked rumors that he might threaten to resign, something he has done before.

For now, the administration’s focus remains on Mr. Netanyahu, whom American officials hope they can persuade to renew the freeze, with the understanding that Washington will ask for no further extensions. The administration’s special envoy to the region, George J. Mitchell, met with Mr. Netanyahu on Wednesday and plans to meet him again before seeing Mr. Abbas on Friday.

Details of the American offer were first reported in the Israeli news media, and widely disseminated in Washington in an essay by David Makovsky, a Middle East analyst at the Washington Institute for Near East Policy.

The White House denied Thursday that President Obama had sent a letter with proposals to Mr. Netanyahu. It declined to comment further on the negotiations.

But on Wednesday, the White House’s senior Middle East advisers, Dennis B. Ross and Daniel B. Shapiro, briefed Democratic representatives on Capitol Hill about what Mr. Ross described as a “string of assurances in return for a two-month moratorium,” according to people who were in the meeting.

These would include additional military equipment — missile systems, aircraft, and satellites — a pledge to help Israel enforce a ban on the smuggling of weapons through a Palestinian state, and a promise to help forge a regional security agreement that would defend Israel against the threat posed by Iran.

Mr. Netanyahu has brushed aside these offers, officials said. For him, said an Israeli official, the political necessity of standing firm on settlements outweighs any security incentives offered by the United States.

“These are wonderful proposals, but because of the political realities, we can’t even have this discussion,” said the official, who spoke on condition of anonymity because of the delicacy of the talks. “It’s a question of what else can be offered.”

Mr. Netanyahu has broached the possibility that the United States release Jonathan Jay Pollard, a civilian intelligence analyst who pleaded guilty to spying for Israel in 1986 and was sentenced to life in prison. Mr. Pollard is a heroic figure in the settlements; winning his release would be a coup for Mr. Netanyahu and could allow him to justify extending the freeze.

But President Bill Clinton rejected a request by Mr. Netanyahu to release Mr. Pollard in 1998, when the prime minister used it as a bargaining chip during previous peace talks. There is little evidence that Mr. Obama would do any different.

Representative Gary L. Ackerman of New York, who was in the briefing, said the length of an extension is another sticking point: the administration is pushing for two months, while Mr. Netanyahu has indicated that he is not willing to go beyond one month, if he agrees at all. If Mr. Netanyahu does accept the administration’s proposal, the hope is that the Israelis and Palestinians would get far enough in two months of negotiations — perhaps even tackling the contentious issue of the borders of a Palestinian state — that neither would want to walk away once the moratorium expired again.

Mr. Abbas said he would consult with the Palestinian movement and the Arab League before deciding his next move. The Palestine Liberation Organization’s executive committee is scheduled to meet Saturday. The Arab League, originally planning a Monday meeting, has delayed it until Wednesday.

But word of the speech by Mr. Abbas has deepened the unease in Jerusalem and Washington. A Palestinian spokesman, Nabil Abu Rudeineh, said he did not know what Mr. Abbas planned to say, but that talk of his resignation was only speculation.

The administration has not yet made a proposal to the Palestinians, according to a Palestinian official. But if Mr. Netanyahu turns down the United States, officials said, Mr. Obama could provide the Palestinians with their own assurance: his formal endorsement of a plan under which Israel’s pre-1967 borders, with land swaps, would form the baseline for negotiations over territory.

Some Palestinians point out that Secretary of State Hillary Rodham Clinton and other American officials, in their public statements, have all but embraced the idea of using the 1967 borders, making a formal endorsement of that position no grand gesture.

Still, that could increase the pressure on Israel; Israeli officials have long fretted that once Mr. Obama puts American parameters on the table, the Palestinians will refuse to accept anything less. And the White House has said that it will wait until negotiations get going before offering any bridging proposals.

Many Palestinians seemed incensed that Israel would get anything more from the United States in exchange for freezing settlements, which are widely regarded as illegal.

“It is like giving a prize to a thief,” said Mustafa Barghouti, a Palestinian politician. “Palestinians want to see their president stand up and say enough is enough.”