The Obama administration formally innaugurated its foray into Middle East peacemaking on Thursday, bringing together the Israeli and Palestinian leaders for face-to-face talks and securing their pledge to meet every two weeks to pursue an end to the decades-old conflict.

At a State Department ceremony, Secretary of State Hillary Rodham Clinton evoked a history of failed efforts to end the Israeli-Palestinian conflict, warning that these negotiations will be no easier. Her husband's Democratic administration and that of Jimmy Carter invested extensive time and prestige to bring about an Israeli-Palestinian peace agreement, as did Republicans George H.W. Bush and George W. Bush. Although some came close, none succeeded.

Clinton encouraged Israeli Prime Minister Binyamin Netanyahu and Palestinian leader Mahmoud Abbas, who flanked her at the head of a large, U-shaped table, to work through the "sabotage" and other challenges that will probably batter the talks in the year ahead.

"By being here today, you each have taken an important step toward freeing your peoples from the shackles of a history we cannot change and moving toward a future of peace and dignity that only you can create," Clinton said. "So thank you - thank you for your courage and commitment."

Clinton's remarks began what is planned to be a year-long negotiation to resolve the conflict's most vexing issues, including the status of Jerusalem, the right of Palestinian refugees to return to homes inside Israel and the future Palestinian state's final borders.

Israelis and Palestinians broke off direct talks in December 2008, and the Obama administration has spent more than a year working to bring the two parties back together.

But many obstacles to a peace agreement remain, and President Obama emphasized Wednesday that "years of mistrust will not disappear overnight." Administration officials, along with the Middle East leaders who have traveled to Washington this week to launch the talks, have sought to manage expectations while also injecting a measure of urgency into the process.

The Palestinian national movement is deeply divided between Abbas's secular Fatah movement and Hamas, the armed Islamist group that killed four Israelis in the West Bank on the eve of new talks. Hamas rejects Israel's right to exist and opposes peace talks.

Netanyahu is managing a fragile governing coalition that includes parties ideologically opposed to the creation of a Palestinian state on territory they claim as the Jewish ancestral homeland.

Within weeks, he must decide whether to extend a 10-month moratorium on settlement construction in the occupied West Bank. Some of his coalition partners have threatened to leave his government, potentially collapsing it, if he does. Abbas has said he might withdraw from the nascent peace talks if Netanyahu doesn't.

The ceremony of the past two days now gives way to what Obama called the "hard work" ahead, facilitated by the United States.

"We believe, Prime Minister and President, that you can succeed, and we understand that this is in the national security interest of the United States that you do so," Clinton said. "But we cannot and we will not impose a solution."

After the morning remarks, Abbas and Netanyahu met with Clinton and Obama's special envoy for Middle East peace, George J. Mitchell, in the secretary of state's outer office. Afterward, the two leaders met alone for an hour and a half.

An Israeli official, who spoke on condition of anonymity because both sides have pledged to keep the talks confidential, said the first meeting went "fairly well." He said Netanyahu and Abbas are determined to "extend a certain commitment to the president at the moment," noting the time and effort that Obama has put into reviving the direct talks.

"He's put a lot of political capital into this, and to see it blow up in a fortnight's time would be very damaging," the official said. "I think both leaders understand this."

Mitchell said the leaders agreed to meet Sept. 14-15 in the Middle East, although the location has yet to be determined. Clinton and Mitchell plan to attend those talks.

Abbas and Netanyahu pledged to meet every two weeks after that to maintain momentum behind the negotiations, which both men have said could be completed within a year.

Mitchell said the leaders decided, as a first stage, to draft a "framework agreement" that will outline the compromises each side must be ready to make to reach a peace agreement.

"You cannot separate process from substance in these negotiations," Mitchell said.

In his opening remarks at the State Department, Netanyahu said, just as Abbas expects Israel to recognize an independent Palestinian state, "We expect you to recognize Israel as the nation-state of the Jewish people."

He called such "mutual recognition" - not only of Israel's right to exist, but to exist as a Jewish state - an "indispensable" element of a final agreement.

About 1 million Israelis, or about 20 percent of the population, are of Arab descent. Abbas has previously resisted the idea of recognizing Israel's Jewish character as part of negotiations, arguing that recognizing its right to exist as a nation is enough. The Palestine Liberation Organization, which Abbas heads, recognized "the right of the State of Israel to exist in peace and security" in 1993.

Abbas, who negotiated several earlier Palestinian agreements with Israel, said the two sides are "not starting from scratch" this round. He called on Netanyahu to "move forward with [Israel's] commitment to end all settlement activities and completely lift the embargo over the Gaza Strip," where Hamas is in power.

Clinton and Netanyahu both cited the recent shooting attack in the West Bank as a reminder of the threats that negotiations will face in the coming months, as groups such as Hamas seek to disrupt the process.

Addressing one of Netanyahu's most pressing concerns, Abbas said security "is vital for both of us, and we cannot allow for anyone to do anything that would undermine your security and our security."

In briefing reporters, Mitchell said one thing he learned from studying previous U.S.-mediated Middle East peace efforts is that "at least in a couple of instances, time ran out."

Both Bill Clinton and George W. Bush began serious pushes for peace with a year left in office. Clinton was still attempting to forge a deal as a lame duck.

"This president, I believe, will succeed," Mitchell said. "But, as he said yesterday, neither success nor failure is predetermined or guaranteed, but it isn't going to be because time ran out at the end."