The Israeli and Palestinian leaders were to open direct peace negotiations Thursday after committing to work to end the conflict that has endured for six decades.

The talks are to be held at the State Department, where they will take place under the eye of Secretary of State Hillary Rodham Clinton. The negotiations follow a remarkable tableau at the White House on Wednesday night, where President Obama, flanked by Prime Minister Benjamin Netanyahu of Israel and President Mahmoud Abbas of the Palestinian Authority, vowed to do everything within his power in the next year to achieve the comprehensive agreement that has eluded negotiators since Israel was established.

“We are but five men,” Mr. Obama said Wednesday night. “But when we come together, we will not be alone. We will be joined by the generations of those who have gone before.”

In somber, emotional tones at the White House Wednesday night, Mr. Netanyahu and Mr. Abbas expressed their own determination to make peace.

Mr. Netanyahu, turning toward to Mr. Abbas, called him his “partner in peace.” He said he came to find a “historic compromise” but warned that any deal must be anchored in ensuring Israel’s security.

Mr. Abbas, for his part, said he would push hard despite “the difficulties we’re going to face tomorrow.” But he quickly foreshadowed the biggest early sticking point in the talks, calling for Mr. Netanyahu to freeze settlement activity in the West Bank.

While the issues are daunting, some analysts also saw a reed of hope in the resolute response of Mr. Netanyahu and Mr. Abbas to the killing by Hamas gunmen of four Israeli settlers in the West Bank on the eve of the talks. Both men immediately said the attack should not be allowed to derail the negotiations, and the Palestinian Authority condemned the killings.

“Normally, it’s been reliably easy to torpedo, or veto, any progress between Israelis and Palestinians,” said Ziad J. Asali, the president of the American Task Force on Palestine. “This means an incredible loss of a weapon.”

On Thursday, a Hamas spokesman said the group was responsible for another attack in which two settlers were shot and wounded just as Mr. Obama began his White House meetings. Reuters quoted a Hamas spokesman in Gaza, Sami Abu Zuhri, as saying “operations of resistance will continue” and neither Israel nor the Palestinian Authority would be able to thwart them.

The East Room gathering was a rare moment of diplomatic theater, endorsed by the attendance of President Hosni Mubarak of Egypt and King Abdullah II of Jordan, and orchestrated by Mr. Obama as part of an effort to invest the process with his own personal stature.

It came after Mr. Obama held a series of one-on-one meetings with the men throughout the day, and just before they were to begin a working dinner.

For Mr. Netanyahu and Mr. Abbas, Thursday’s talks, with their very real chance of failure, represent a huge risk: President Bill Clinton’s failed attempt in 2000 led to the Palestinian intifada while President George W. Bush’s Annapolis peace attempt dissolved amid chronic violence in Gaza.

“Too much blood has already been shed, too many hearts have already been broken,” Mr. Obama said. “This moment of opportunity may not return soon again.”

The inclusion of Mr. Mubarak and King Abdullah underlines the administration’s hopes to forge a regional solution to the conflict. Egypt and Jordan are critical to providing Israel with security guarantees that would enable it to accept the creation of a Palestinian state.

Mr. Mubarak has offered to host subsequent rounds of talks in Egypt, though officials said he was pushing for Mr. Obama to take a direct personal role in the process. The standing of Mr. Mubarak, 82, in the region is such that officials said the administration was eager to get direct talks going quickly, because his health is said to be fragile and the United States is worried about the uncertainty that will come after he passes from the scene.

Jordan is a crucial player because of the difficult question of how to secure its border with a new Palestinian state. Israel currently has troops along that frontier and would balk at withdrawing them without a guarantee that the border would not become a conduit for missiles that militant groups opposed to the peace process, chiefly Hamas, could fire at Tel Aviv and other cities in Israel.

Previous attempts to involve Israel’s Arab neighbors in constructing a peace deal between Israelis and Palestinians have fared poorly. Mr. Obama’s most recent attempt, when he sought to win confidence-building measures from Israel’s neighbors like allowing Israeli carriers to fly over their countries, failed when Saudi Arabia and other Arab states refused.

But more recently, the Saudis pressed Mr. Abbas to agree to the direct talks, using their financial aid to the Palestinian Authority as a lever.

The Arab League also has put its stamp of approval on the negotiations.

The success of the talks, all sides said, will depend in part on whether Mr. Obama can succeed where his predecessors have failed in pushing Palestinians and Israelis toward resolving the core final status issues that have bedeviled peace negotiators since 1979.

Those issues include the dismantling of Israeli settlements in the West Bank, the borders of a Palestinian state, the security of Israel, the status of Jerusalem and the fate of Palestinian refugees who left, or were forced to leave, their homes in Israel.

Mr. Obama will know quickly whether he has any more chance of success than the eight failed attempts that have gone before this one. At the end of September, Israel’s 10-month moratorium on settlement construction will expire. Mr. Netanyahu so far has not indicated any willingness to extend it, and Mr. Abbas has said that he will withdraw from negotiations if settlement activity resumes.

American officials have been working with their Israeli and Palestinian counterparts to try to come up with a way around the issue to no avail so far.

During the meeting on Wednesday afternoon between Mr. Obama and Mr. Abbas, American officials said they would press the Israelis to find a way around the moratorium expiration, but they also asked the Palestinian president to try to be flexible, according to advisers to all three sides.

Mr. Netanyahu made no specific mention of settlements during his remarks before the dinner. The closest he came was in an acknowledgment of Palestinian claims to land.

“The Jewish people are not strangers in our homeland, the land of our forefathers,” he said. “But we recognize that another people share this land with us. And I came here today to find a historic compromise that will enable both peoples to live in peace, security and dignity.”

For Mr. Obama, the settlements issue is doubly important because if it blows up the talks, Middle East experts said, he will once again have left the perception in the Arab world of escorting Mr. Abbas out on a limb and then leaving him there.

Many Palestinian officials complain that Mr. Obama’s decision last year to drop his demand for Israel to halt settlement construction as a prelude to peace talks may have delayed the start of these negotiations, since it was difficult for the Palestinian leader to back down.