The peace talks launched by the Israeli and Palestinian leaders Tuesday face a daunting array of obstacles. They will be overseen by two men who are weakened by extremists at home and speak for peoples whose attitudes toward each other have hardened since the last effort collapsed nearly seven years ago.

Mahmoud Abbas, the Palestinian Authority president, controls only part of his would-be state. Israeli Prime Minister Ehud Olmert's coalition government faces a threatened walkout by right-wing parties that could bring it down.

And though the two have developed a rapport over the last 11 months, the peace negotiations will require complex and delicate arrangements and a level of trust that does not exist between their teams.

The procedure for the negotiations, scheduled to start Dec. 12 in Jerusalem, took two months to hammer out. And it was produced only on Tuesday due to last-minute U.S. intervention. That does not augur well for talks that lie ahead on the core issues, because the Bush administration says it will remain mostly on the sidelines.Those issues include the borders of a new Palestinian state, rival claims to Jerusalem and the fate of refugees who fled their homes during Israel's 1948 war for independence.

But the talks are likely to focus initially on reviving a 2003 U.S.-backed plan known as the "road map" that calls for simultaneous steps to ease tensions on the ground and pave the way to compromise.

Previous negotiations over the last two decades have suggested workable solutions on each of the core issues. But Olmert and Abbas are burdened by the failures of those efforts.

Their impassioned but wary exchange Tuesday, as they shared a stage with President Bush, pointed to the difficulties ahead.

"The memory of failures of the near and distant past weighs heavily upon us," Olmert said. "The dreadful terrorism perpetrated by Palestinian terrorist organizations has affected thousands of Israeli citizens, destroyed families and attempted to disrupt the lives of all citizens of Israel."

"These are factors which deter us from moving forward too hastily," he added.

At his turn to speak, Abbas tried to assure Olmert that he was "committed to fight lawlessness." In return, he demanded swift completion of a deal to end Israel's 40-year-old occupation of the Palestinian territory.

"I have to defend the right of my people to open their eyes to a new dawn free of occupation, settlements, apartheid walls, prisons full of prisoners, targeted assassinations, and the siege of checkpoints around villages and cities."

"Our people," he added, "clearly understand the difference between the threat posed by terrorism versus using terrorism as a pretext to maintain an intolerable situation."

That impasse has bedeviled negotiators for years, most recently at Camp David in 2000 and Taba, Egypt, in 2001.

By pledging to honor the long-ignored road map, the two leaders in effect have agreed to stop the attacks and begin an Israeli withdrawal from Palestinian territory while simultaneously trying to negotiate the major issues.

Although they agreed to take such steps under U.S. supervision, there is no explicit American commitment to press either side publicly for not complying.

That will leave both leaders vulnerable to fierce opposition at home, where the hard compromises required during peace talks will challenge their hold on power.

Olmert has only recently begun to speak publicly about concessions Israel is expected to make. Abbas said almost nothing until Tuesday.

Risking wrath from hawkish critics at home, Olmert pledged Tuesday that Israel would try to reach an accord by the end of next year on the core issues.

But at Israel's insistence, the two sides agreed that implementation of a final accord -- and the birth of a Palestinian state -- must wait until each side complies fully with the road map.

That plan requires the Palestinians to "take steps to dismantle terrorist organizations" -- in other words, a victory by Abbas' Fatah party over the militant group Hamas, which calls for Israel's destruction.

Whether Abbas' government is capable of doing that is a matter of fierce debate and is certain to be a crucial theme in the negotiations.

Abbas has lost much of his authority since his election in 2005. Hamas drove his forces from the Gaza Strip in a battle in June. Even before then, Hamas and other groups were defying him by firing rockets almost daily from Gaza, terrorizing Israeli communities.

Abbas' government now rules only the West Bank, but even there it faces potential attacks by Hamas gunmen lying low.

"He will be trying to negotiate the future of the Palestinian people while he is literally at war with at least half of [them]," said Bruce Riedel, a former intelligence official now at the Brookings Institution.

Hamas branded Abbas' pledges at Annapolis a crime and threatened new violence if he makes concessions.

In recent months, Abbas has moved to demonstrate to Israel that he's serious about asserting control, starting in the West Bank. He has deployed hundreds of extra police officers to the unruly city of Nablus. He has closed dozens of Hamas charities, fired Hamas preachers, arrested hundreds of Hamas activists, including many gunmen, confiscated weapons and issued a decree aimed at drying up millions of dollars in donations to Hamas from abroad.

But Israeli officials and Western observers say he is nowhere close to forming a reliable, effective security apparatus to take over the West Bank from Israeli troops. Israel, which occupied the West Bank and Gaza as a result of the 1967 Middle East War, withdrew from Gaza in 2005, taking apart the enclave's security apparatus.

"Signing a permanent status agreement with the weak Abbas is like building a multistory building without foundations," Benjamin Netanyahu, leader of Israel's right-wing opposition Likud Party, said Tuesday. "Sooner or later this building will collapse on us."

The criticism was echoed inside Olmert's broad-based but shaky coalition government. Eli Yishai, leader of the right-wing Shas party, threatened to pull out of the government if the rockets from Gaza don't stop when the negotiations start.

Olmert addressed part of his speech Tuesday to his critics at home, saying he recognizes "all the obstacles which are sure to emerge" as talks proceed.

But he said Israelis must prepare to make concessions, alluding to a withdrawal from the West Bank that will be "extremely difficult for many of us" but "nevertheless inevitable."

It remains to be seen, however, whether Olmert can even take the first step of the road map -- freezing the growth of West Bank settlements where 267,500 Jews now live and tearing down smaller settler outposts -- without bringing down his coalition.

In the run-up to Tuesday's conference, Israel's parliament moved to tie Olmert's hands by tentatively approving a bill barring any agreement to another Palestinian demand: to divide Jerusalem.

Another thorny issue is the fate of more than 4 million Palestinians whose families fled what is now Israel in 1948. Abbas insisted Tuesday on their "right of return" to their homes. Israelis oppose any return of Palestinian refugees, fearing that the influx could give Arabs a majority and lead to destruction of the Jewish character of the state.
In his speech Tuesday, Olmert insisted three times on explicit Palestinian recognition of the right of two peoples, Jews and Palestinians, to have separate states.

But the biggest obstacle in the peace talks is each side's anxiety over the other's willingness and ability to implement a deal. Israel Radio released a poll Tuesday showing 62% of Israelis support a negotiated peace, but the same number don't believe it will happen this generation.