Secretary of State Hillary Rodham Clinton is expected to announce Friday that Israel and the Palestinians will return to direct negotiations for the first time in 20 months, delivering the Obama administration a small victory in its protracted effort to revive the Middle East peace process, two officials briefed on the situation said Thursday evening.

The Israeli prime minister, Benjamin Netanyahu, and the president of the Palestinian Authority, Mahmoud Abbas, have agreed to place a one-year time limit on the talks, these officials said.

President Obama is expected to invite both leaders to Washington in early September to start the negotiations, which will cover thorny issues like the borders of a new Palestinian state, the political status of Jerusalem, security guarantees for Israel and right of return for Palestinian refugees.

The Obama administration declined to confirm the announcement with an official cautioning that final details were still being worked out and that the timing could slip by a day or so.

But after months of grueling diplomacy by the administration’s special envoy to the region, George J. Mitchell, officials sounded a more optimistic note on Thursday.

“We think we are very, very close to a decision by the parties to enter into direct negotiations,” Philip J. Crowley, the State Department spokesman, said to reporters. “We think we’re well positioned to get there.”

Mrs. Clinton has been working the phone in recent days to clear the final hurdles, speaking Thursday with Jordan’s foreign minister, Nasser Judeh, and with Tony Blair, the special representative of the Quartet, the group of Middle East peacemakers comprising the United States, the United Nations, the European Union and Russia.

Late on Wednesday, she spoke with the prime minister of the Palestinian Authority, Salam Fayyad. The official Palestinian news agency Wafa reported that on Thursday night President Abbas called a meeting of the Fatah Central Committee, the party’s main decision-making body, at which “developments in the peace process” were discussed.

While the details of the talks are not yet public, the one-year time limit is viewed as crucial because the Palestinians are leery of being drawn into an open-ended negotiation with Israel. Mr. Netanyahu has long said he is open to talks, but the Palestinians have been resistant, seeking assurances from the United States about the terms and conditions.

Israel has eschewed any pre-conditions to negotiations, officials said, including an extension of the government’s 10-month, partial moratorium on settlement construction in the West Bank, set to expire on Sept. 26. The Obama administration has pushed to restart direct talks so that the two sides would be at the negotiating table when that date arrives.

Mr. Obama held separate meetings with Mr. Netanyahu and Mr. Abbas in recent weeks, which officials said helped reassure the Palestinians and began to heal a rift between Israel and the United States over American demands that Israel halt settlement construction.

The broad outlines of a peace agreement are well known and likely to be based on the borders of Israel before the 1967 Arab-Israeli war, with certain agreed-upon land swaps. But many analysts are skeptical that Israel and the Palestinians will be able to reach a deal, given the hardened political realities on each side.

Mr. Netanyahu is trying to hold together a right-wing coalition that will view concessions, like an extension of the settlement moratorium, with extreme suspicion. The Palestinians are deeply divided between Fatah, which controls the Palestinian Authority from its base in the West Bank, and Hamas, a militant Islamic group that rules Gaza and is shunned by the West for its terrorist attacks.

Some analysts believe the two sides will quickly turn to the United States to provide “bridging proposals” to help close the gap on delicate issues. Mr. Crowley stressed that the negotiation was between Israel and the Palestinians, but acknowledged the American role.

“We, the United States, have always played a special role within this effort, and we will be prepared to assist the parties going forward in moving towards a successful negotiation,” he said.