The chief Palestinian negotiator said Monday that he believed reaching an agreement with Israel within a year was “doable,” echoing remarks by the Israeli prime minister a day earlier that a peace agreement would be difficult but “possible.”

But the otherwise sharply differing declarations presented as the basis for going into the direct talks, scheduled to start in Washington on Sept. 2, reflect the complexity of the effort required to get the two sides to this point, and the daunting challenges that lie ahead.

At a news conference here at the administrative headquarters of the Palestinian Authority, Saeb Erekat, the chief negotiator, said the leadership had accepted the invitation to return to direct talks, which broke off in late 2008, based on the statement issued Friday by the so-called quartet of Middle East peacemakers: the United States, the United Nations, the European Union and Russia.

When asked what had changed to move the Palestinian leadership to return to direct talks, despite what appeared to be only a vague international response to Palestinian demands for assurances on the talks’ goal, he pointed again to the quartet’s statement.

“This statement was not there on Aug. 19,” Mr. Erekat said, “only on Aug. 20.”

Earlier this month, the Palestinian Authority president, Mahmoud Abbas, complained to reporters in Ramallah that he was under almost unbearable international pressure to return to direct talks.

The quartet’s statement, issued alongside the announcement of the start of talks by Secretary of State Hillary Rodham Clinton, was intended to satisfy Palestinian demands for terms of reference for the talks, given that Israel and Mrs. Clinton rejected any “preconditions.” The Palestinians wanted assurances that the goal of the talks would be a Palestinian state based on the pre-1967-war lines and that the talks would be accompanied by a freeze of all Israeli settlement construction.

In reality, the carefully worded statement was itself a compromise. It reaffirmed the quartet’s commitment to previous statements, which called for a settlement that “ends the occupation which began in 1967” and results in the emergence of a Palestinian state, and which called on Israel to freeze all settlement activity and to refrain from demolitions, evictions and other provocative acts in East Jerusalem.

But the quartet’s statement made no new, explicit call for a settlement freeze, adding to a cloud of uncertainty hanging over the talks.

The first major test for the Israeli prime minister, Benjamin Netanyahu, is expected around Sept. 26 when Israel’s partial, 10-month moratorium on settlement construction is to expire.

“If Mr. Netanyahu decides to renew settlement tenders come Sept. 26, he will have decided to stop negotiations,” Mr. Erekat said. He added that Mr. Abbas had sent letters to President Obama and other quartet leaders urging them to take a “strong and unequivocal position regarding Israel’s obligation to freeze all settlement activity, without exceptions.”

Mr. Netanyahu faces tough internal opposition from his right-wing ministers to any extension of the moratorium; it was under intense American pressure that he persuaded them to back the temporary, partial freeze in the first place. One minister, Dan Meridor, has proposed a formula whereby Israel would build only in the settlement blocks it intends to keep under any deal.

A State Department spokesman, Philip J. Crowley, said Monday that the United States was “very mindful” of this issue and that it would be “among the topics discussed early on” in the negotiations.

In remarks at the start of the cabinet meeting in Jerusalem on Sunday, Mr. Netanyahu did not mention the settlement issue, but said a historic agreement with the Palestinians would be based on “three initial components”: sustainable security arrangements; recognition of Israel as the “national state of the Jewish people,” meaning that any return of Palestinian refugees would be “realized in the territory of the Palestinian state”; and the end of conflict between Israel and a demilitarized Palestinian state.

Mr. Erekat said that amounted to Mr. Netanyahu’s setting conditions for the outcome before having started the talks. “It seems that he wants to negotiate with himself and his coalition,” Mr. Erekat said.

Both Mr. Netanyahu and Mr. Erekat addressed the skepticism and frustration among their respective publics after 17 years of an on-and-off peace process. Both also said they hoped to find a true partner on the other side.

Mr. Abbas comes to the talks in a particularly weak position, having lost control of Gaza to Hamas, the Islamic militant group. Hamas defeated Mr. Abbas’s Fatah party in parliamentary elections in 2006, then routed forces loyal to Mr. Abbas from Gaza after months of bloody factional fighting in 2007.

Mahmoud al-Ramahi, a Hamas-affiliated politician, is the general secretary of the Palestinian Legislative Council, or Parliament. He said in Ramallah on Monday that from Hamas’s point of view, negotiations with Israel were “useless” and would not lead anywhere. But he said that Mr. Abbas and the Palestinian Authority had no alternative but to go to the negotiations, since they rely so heavily on the West for financial support.