JERUSALEM — Intensive efforts are under way to stave off a Palestinian bid for United Nations membership in September, with diplomats trying to lure Israeli and Palestinian leaders back to negotiations on the basis of President Obama’s formula of a state based on the 1967 lines with mutually agreed land swaps.

Israeli and Palestinian leaders have told American and European officials who have been here repeatedly in recent weeks that they want to return to talks. But with numerous moving parts, neither side desperate about the status quo and no agreement on the terms, success is far from assured.

The Israeli government was livid about Mr. Obama’s reference to the 1967 lines and swaps in a speech in May. It considers those boundaries indefensible and does not want to commit in advance to giving up land within Israel in exchange for keeping settlement blocs in the West Bank.

But Israeli officials acknowledge that they have little choice but to work within that formula as a negotiating basis if they want to stop the move in the United Nations. A successful General Assembly vote for the Palestinians could increase boycott and sanctions pressure on Israel as well as international legal proceedings in forums like the International Criminal Court.

“The goal is to get something on the table that keeps September from happening and that is an initiative Israel can live with,” a top Israeli official said, speaking on condition of anonymity because of the secretive and sensitive nature of the diplomacy. “For us, that would be an acknowledgment of Jewish sovereignty.”

Prime Minister Benjamin Netanyahu of Israel referred to the same issue in a speech here on Thursday night. Mr. Netanyahu said that the end of the conflict with the Palestinians would begin when their leaders uttered six words: “I will accept the Jewish state.”

Two other issues that would mollify the Israelis are an assertion that Palestinian refugees from the 1948 war of independence would be permitted to settle in a future state of Palestine but not in Israel itself, and a reference to an Israeli security presence along the Jordan River.

For their part, the Palestinians have said they need two conditions to restart talks — a reference to the 1967 lines as the basis for their state and at least a short stoppage of Israeli settlement building in the West Bank. Having received the first from President Obama, some Palestinian officials are saying they might drop the second.

But they say they will not accept Israeli soldiers on their future land, or call Israel a Jewish state, or give up in advance any Palestinian refugee right of return to their original homes inside Israel. To do so, they say, would be to prejudice the rights of Israel’s 1.4 million Arab citizens and walk away from the rights and interests of millions of Palestinians abroad.

“No Palestinian leader can abandon the right of return,” Muhammad Shtayyeh, a member of the Fatah Central Committee and an adviser to President Mahmoud Abbas of the Palestinian Authority, said in a telephone interview.

American officials are examining the possibility of inviting the two sides to talks in a document that lays out a number of these conditions as American goals while allowing each to accept the invitation without signing off on every condition, but they acknowledge that would be a weak basis for talks.

Some Palestinian officials say that even if peace talks get going this summer, the move toward United Nations recognition will proceed. But American and European officials believe that Mr. Abbas is having second thoughts.

This is because American officials have told him that Washington would veto any Palestinian membership bid in the Security Council and work to reduce the number of supporting votes there and in the General Assembly. Some European states — Germany, Italy and several from Central Europe — have expressed their opposition and hope to pressure the Palestinians back into negotiations. Canada, which is also strongly opposed, has been lobbying smaller countries to tell the Palestinians that they will not to vote with them in September.

Catherine Ashton, foreign policy chief for the European Union, told the newspaper Haaretz this week that the United Nations vote on Palestinian statehood was far from a done deal.

As a result, what looked several months ago like near-certain Palestinian victory and Israeli defeat at the United Nations seems less clear today, officials from several countries say, and the Palestinians are reconsidering.

Mr. Abbas and his aides also worry that their people could build up unreasonable expectations over a move at the United Nations and wake up frustrated and angry the day after a vote to discover that little had changed on the ground. They fear the possibility of violence erupting.

But another issue threatening the current effort is the possibility of a Palestinian unity government being formed between Mr. Abbas’s Fatah and Hamas, which rules in Gaza.

Even though such a government would be made up of technocrats without affiliation to either group, a Hamas sponsorship of a new Palestinian government could prompt the United States and possibly Europe to cut off aid because both consider Hamas a terrorist group.

Israeli officials say that if the unity deal goes through, it would end any chance of talks and that they feel confident that Washington will back them on that decision.

Since relations between Fatah and Hamas are strained and Mr. Abbas is worried about aid being cut off, the unity talks have stalled and seem likely to stay that way until it is clear whether the effort to get the Palestinians and Israelis back into negotiations will succeed or fail.