UNITED NATIONS — The U.N. Security Council should send a U.N. peacekeeping force to Gaza, where it could help to maintain a future truce between Israel and armed groups there, the Palestinian Arab observer at the United Nations, Riyad Mansour, said yesterday.

The proposed contingent, modeled after the recently enlarged U.N. Interim Force in Lebanon, was suggested as Prime Minister Olmert said he is hoping to conduct an unprecedented meeting with Prime Minister Siniora of Lebanon, in an attempt to broker a peace agreement between the two countries.

Mr. Olmert told Israel’s Channel 2 TV that at his request, “two top world leaders” are conducting negotiations to set up such a meeting. However, Mr. Siniora, who is facing a tough challenge from Hezbollah, has repeatedly dismissed the idea of a meeting with his Israeli counterpart.

The White House announced yesterday that Mr. Olmert will visit President Bush in Washington on Monday. In addition to the situation in Lebanon, the two are expected to discuss Gaza, which has seen its increasingly bloody clashes broadcast on TV screens around the world.

“It is high time” for a Security Council intervention to “stop immediately the Israeli atrocities,” the Palestinian Arab president, Mahmoud Abbas, wrote in a letter to the council’s rotating president, which is now Peru. The Arab group at Turtle Bay wants to convene the council as early as today, diplomats say.

One of the ideas the Palestinian Arabs will promote, Mr. Mansour said, is to declare a “mutual cease-fire” between the Israel Defense Force and the armed groups that have used Gaza as a base for rocket attacks against Israeli border towns since the Israeli withdrawal from Gaza in August 2005.

Once such a cease-fire is agreed on, the U.N. force would be brought in to ensure that both sides observe it, he said. Direct negotiations between the sides could lead to a comprehensive agreement later. The U.N. force, according to Mr. Mansour, could be modeled after UNIFIL, which was deployed in August and currently encompasses 9,450 troops from 20 countries, according to U.N. numbers released yesterday.

“If it worked for Lebanon in that context, it could be possible it would work” in Gaza as well, Mr. Mansour said.

Israeli officials, however, say that before negotiations can resume, the Palestinian Arabs have to prove that they can control the terrorists. The Hamas-led government also has to agree to demands from the United Nations, Russia, the European Union, and America, collectively known as the Quartet. Their requirements include recognizing the Jewish state and previous signed agreements, as well as renouncing terrorism.

By calling for the United Nations to intervene, “the Palestinian government sheds its responsibility to control the areas and people under its jurisdiction,” the deputy Israeli ambassador to the United Nations, Daniel Carmon, told The New York Sun.

Negotiations between Mr. Abbas, who leads the Fatah Party, and Prime Minister Ismail Haniyah of Hamas failed to yield an agreement last night on a “unity government.” An Israeli official who spoke on condition of anonymity told the Sun that even if it is established, such a government is unlikely to agree to the Quartet’s conditions.

A deputy State Department spokesman, Tom Casey, said in a statement that the unity government “needs to accept” the Quartet’s requirements. In Washington yesterday, Secretary of State Rice answered those critics who contend the Bush administration’s push for Middle East democracy has only increased the power of extremists like Hamas.

“I’m not so sure that it is better to have these groups running the streets, masked, with guns, rather than having them have to face voters and having to deliver,” Ms. Rice said. “So when I am told, ‘Well, you know your Middle East policy has allowed Islamists to come to power,’ I think, well, all right, so was the answer, then, that the people of the Middle East don’t get to have a voice in who comes to power?”