Palestinian leaders have already endorsed the plan, known as the road map. With rapid, reciprocal concessions, it seeks not only to end 31 months of conflict but also to resolve territorial and religious claims that have divided the two peoples for generations.

Mr. Sharon plans to present the agreement to his government by Sunday or Monday, Israeli officials said, calling the American assurances that Israel's concerns would be addressed the minimum help he needed to win a majority. Many of the 23 ministers oppose a Palestinian state, and reject the plan as a danger to Israel. Sharon allies said tonight that the plan's approval was likely but not assured.

The White House said that Israel's endorsement might pave the way for a summit meeting of President Bush, Mr. Sharon and the Palestinian prime minister, Mahmoud Abbas.

Today, in Crawford, Tex., Mr. Bush said that Mr. Sharon made his endorsement because of American assurances of a commitment to Israel's security. He said that "since we're committed to Israel's security, as we move forward we will address any concerns that might arise."

Having coaxed forward a new Palestinian leader, Mr. Abbas, and persuaded Mr. Sharon to embark on the peace plan, Mr. Bush appeared to be plunging his administration into the detail of Middle East peacemaking. Palestinians and Israelis disagree on almost all elements of the plan, and they will look to the president to arbitrate their disputes — beginning with whether Israel will get the changes it wants.

Secretary of State Colin L. Powell said today that Israel's concerns could be met without changing the plan. Asked if the United States was not kicking problems down the road by pushing Israel to endorse the plan before resolving its concerns, Mr. Powell said on his plane returning from Paris: "At least we have a can in the road. It's easy to say, `Why didn't you solve this all up front?' Because you couldn't. You couldn't get started."

He added that now "the can is in the road and we will start moving it down the road, perhaps with little kicks, as opposed to a 54-yarder."

Palestinian officials, while welcoming Mr. Sharon's announcement, said that the letter of the plan had to be obeyed. But Raanan Gissin, a Sharon spokesman, said that both sides would have to accept adjustments. 

"It's not the Ten Commandments from Mount Sinai," he said. "It only sketches in broad strokes the phases and sequences in order to reach President Bush's vision."

Israel wants to see the Palestinians crack down on violence and confiscate illegal weapons, as called for in the plan's first phase, while deferring some of its own first-phase obligations, like a settlement freeze. But while Israelis are focused on achieving security, Palestinians are eager for political progress.

For example, as the first Palestinian step, the plan calls for a declaration of an unconditional cease-fire, and a declaration by Israel "affirming its commitment" to a two-state solution including "an independent, viable, sovereign Palestinian state." 

The Palestinians want those statements made, believing the explicit Israeli commitment would strengthen Mr. Abbas as he moves against terrorism. But it is a politically difficult step for Mr. Sharon. 

Mr. Gissin said action mattered more than words. "The declarations come later, and the farther we move away from declarations the better," he said. "Let's start doing."

The language in Mr. Sharon's announcement — explicitly accepting the "steps" of the plan, not the plan itself or its goals — was no accident, his allies said. Rather than the swift resolution of all disputes sought by the plan, Mr. Sharon wants a long-term "interim solution" before full Palestinian statehood, arguing that it will take many years for the two peoples to learn to live together peacefully.

After the first phase of six months ends, the second envisions a Palestinian state "with provisional borders and attributes of sovereignty" before the two sides move on six months later to the third phase, to negotiate precise borders, control of Jerusalem and other matters.

Mr. Abbas is said by associates to hate the idea of a provisional state. He is said to fear that once it is achieved it will downgrade the Middle East dispute to just another argument over borders, slowing momentum to full Palestinian statehood. But the provisional state sounds a bit like Mr. Sharon's interim agreement.

"If you're stuck in Stage 2," one associate of Mr. Sharon said, "then maybe the Palestinians don't have everything they wanted, but their lives are better than before. And then we wait a little longer to achieve the third phase."

The plan was drawn up by a diplomatic "quartet" of the United States, the United Nations, the European Union and Russia.

In broad terms, the Israelis want movement from one stage to the next to be determined by performance only, while the Palestinians want to see progress according to the plan's timetable. The Israelis say that only full compliance with all obligations can secure lasting peace, while the Palestinians say that only a strict timetable can prevent extremists from sabotaging progress.

Acceptance of the peace plan could break Mr. Sharon's coalition by disappointing two parties allied with the settlers movement in the West Bank and the Gaza Strip. But leaders of those parties will have to weigh whether they will have more influence over the plan's realization by staying, or by leaving and watching Mr. Sharon inevitably turn for support to the left-leaning Labor Party.

If Labor joins the government, the settlers could well see Shimon Peres, Labor's inveterate peacemaker, return to his post as foreign minister. 

"They will feel for a moment pure and ideological," Nahum Barnea, political columnist for Israel's largest daily newspaper, Yediot Ahronot, said of the far-right leaders. "But afterward they will get only negative reactions from their voters."

Mr. Sharon could also face a revolt within his own party, the dominant Likud. Meir Sheetrit, a Likud minister, said that the prime minister "will have problems," but that he would probably gain enough support in the end. 

It is not a good moment for Likud rivals to challenge Mr. Sharon. He is overwhelmingly popular, and Israelis are impatient for any improvement in their economy or security. Further, they trust Mr. Bush.

Mr. Sheetrit has been a lonely voice in his party demanding action on the peace plan. "In my opinion, we are quite strong enough, in order to be generous," he said, adding that the Palestinians would have to prove themselves a worthy partner.

He said of Mr. Sharon, "I believe he has one time in life to really change the situation in the area, and to write a chapter in this history of the state of Israel."

But Yuval Steinitz, a Likud leader in the Israeli Parliament, said that Israel was merely getting what it was supposed to gain from the Oslo accords of 1993 and 1995 — an end to terrorism — while the Palestinians were receiving far more: full statehood, without explicit curbs on an eventual military force.

"It is rewarding terrorism," he said. "I will speak against it, I will vote against it. It's impossible." 

Mr. Abbas has his own political problems. Reluctantly appointed under international pressure by Yasir Arafat, he has little popular support. Mr. Arafat retains a great deal of control, and may feel little incentive to promote a diplomatic process that marginalizes him.

Fearing a Palestinian civil war, Mr. Abbas has resisted a crackdown on violent groups, trying instead to negotiate a truce, which Israel fears will only give them time to rearm.