President Mahmoud Abbas of the Palestinian Authority beseeched a group of visiting American Jews on Sunday to urge Congress not to cut off hundreds of millions of dollars in aid as a result of his recent unity agreement with Hamas, the Islamist group that controls Gaza.

“We need your help with Congress,” Mr. Abbas told the visitors from J Street, a group that calls itself pro-Israel and pro-peace. “I hear rumors that Hamas will be in the West Bank, or that it will share authority here. This will not happen. The new government will comply with my policies, and I am against terror and violence.”

Jeremy Ben-Ami, the president of J Street, said he would “bring back to Washington the message that this may be the last opportunity with a Palestinian leader willing to say yes to peace with Israel.” He said he would urge the White House to offer a plan to create a Palestinian state based on the 1967 lines with agreed-upon land swaps and a request of Israel to pause West Bank settlement building for two to three months.

Those are the two conditions under which Mr. Abbas told the group that he would return to peace negotiations with Israel.

“This is our first choice, negotiations,” Mr. Abbas told the group at a lunch he hosted at his West Bank headquarters.

“If we were to start now in negotiations, we would not pay any attention to September,” he added, in reference to the Palestinians’ plan to ask the United Nations to recognize their state this year at its General Assembly meeting if no progress is made by then.

For its part, Israel says it has long advocated beginning talks right away without preconditions, and it contends that Mr. Abbas, with his demands for specific borders and halts on construction, is the one causing delays and lacking in seriousness.

Prime Minister Benjamin Netanyahu of Israel is due to visit President Obama at the White House on May 20 and to address a joint session of Congress the following week. It is unclear if he will lay out a new proposal for how to restart talks, but moving peace negotiations forward will be the focus of the visit.

Ten days ago, Mr. Abbas’s Fatah party, which controls the West Bank, and Hamas made a surprise announcement that after four years of bitter division, they had agreed to establish a unity government of technocrats aimed at holding elections within a year and rebuilding Gaza. Mr. Abbas said that without national unity, a deal with Israel would produce little.

But because Hamas is labeled a terrorist group by the United States, some senators and representatives have expressed deep misgivings. On Friday, 27 senators sent Mr. Obama a letter urging him to halt aid to a unified Fatah-Hamas government unless all of its members renounce violence and recognize Israel. The administration has said it is waiting for more details before judging the new arrangement.

Mr. Abbas reiterated that the members of the new unity government would be affiliated with neither Fatah nor Hamas, that he would continue to set policy and that nothing in the West Bank would change regarding security and cooperation with Israel in the coming year leading up to the election. Israel has denounced the deal as bringing terrorists into the Palestinian government, and for that reason it has delayed handing over Palestinian tax receipts to the Palestinian Authority.

Mr. Abbas made clear that many details remained to be negotiated with Hamas. It also seems likely that he will face compromises. At the ceremony on Wednesday in Cairo, for example, Mr. Abbas originally insisted that the leader of Hamas, Khaled Meshal, neither sit on the podium nor make a speech. He won the argument over the seating, but Mr. Meshal was permitted a short talk.

Mr. Meshal said in an interview on Thursday that Hamas was committed to working with Fatah toward a Palestinian state within the 1967 lines and that together they would decide what kind of resistance to Israel was appropriate.

But he pointedly declined to say that such a state would mean the end of his movement’s dispute with Israel nor would he declare his opposition to the use of violence.

Asked if he thought nonviolent resistance was a useful approach for the Palestinians, he replied, “Unfortunately, nonviolence doesn’t work against the Israelis.”