A day after the main Palestinian factions signed a unity agreement in Cairo, Secretary of State Hillary Rodham Clinton strikingly refused on Thursday to rule out further negotiations with a Palestinian side that includes Hamas, the militant Islamic group that runs Gaza and is defined by many in the West as a terrorist organization. But she reiterated the Obama administration’s call for Hamas to accept basic conditions that included renouncing violence and recognizing Israel’s right to exist.

Mrs. Clinton spoke in Rome before a meeting on Libya as the leading protagonists in the Middle East conflict set out elsewhere to pursue their rival campaigns for sympathy and support on a larger stage, seeking European backing for their conflicting visions of peace and Palestinian statehood.

In Paris, Prime Minister Benjamin Netanyahu was set to meet President Nicolas Sarkozy while the Palestinian leader, Mahmoud Abbas, was expected in Berlin to talk with Chancellor Angela Merkel. The encounter in the German capital will come just 24 hours after Mr. Abbas, the leader of the Western-backed Fatah movement that holds sway in the West Bank, joined forces with Khaled Meshal, the leader of Hamas.

Speaking of the unity pact, Mrs. Clinton said there were “many steps that have yet to be undertaken in order to implement the agreement” when asked if it closed the door on negotiations for an Israeli-Palestinian peace for the foreseeable future. “And we are going to be carefully assessing what this actually means because there are a number of different potential meanings to it, both on paper and in practice.”

In Washington, the administration has already faced calls from members of Congress to suspend American assistance to the Palestinian Authority on the West Bank, led by Mr. Abbas.

The United States has spent $542 million since 2005 to train the Palestinians’ National Security Force, including $150 million in the current fiscal year. Administration officials have said the aid will continue as long as Mr. Abbas and Prime Minister Salam Fayyad remain in charge of the Palestinian Authority as it is now constituted.

At a joint news conference in Rome, Italy’s foreign minister, Franco Frattini, echoed Mrs. Clinton’s caution, saying Hamas had to abide by the conditions outlined by the so-called quartet of Middle East peace mediators to be considered “a possible interlocutor.” Like many American officials, he seemed uncertain that the reconciliation would last.

On Wednesday, Mr. Netanyahu, the Israeli prime minister, in London to meet David Cameron, his British counterpart, labeled the unity deal a “tremendous blow to peace and a great victory for terrorism,” illustrating the gulf between Palestinian and Israeli strategies and perceptions. Hamas is sworn to Israel’s destruction and Israel, like the United States and the European Union, classifies the group as a terrorist organization and refuses any dealings with it.

While Mr. Abbas seemed certain to laud the advantages of Palestinian unity, European aversion to Hamas may well make Mr. Netanyahu’s mission easier, analysts in Paris said, though many European countries, including France, have been largely sympathetic to the Palestinian cause.

The European diplomacy on Thursday came under the looming shadow of several other events scheduled for this year.

This month, Mr. Netanyahu is to meet President Obama at a time when the American president is buoyed by the killing of Osama bin Laden in Pakistan and has emerged as a sponsor of the Arab pro-democracy movements sweeping the region from Libya to Syria to Yemen. One result of the upheaval has been the creation of a new Egyptian leadership that replaced the ousted Hosni Mubarak and has sponsored the Palestinian unity pact.

Beyond that, in September, the United Nations is to consider the fraught issue of declaring recognition of a Palestinian state — a prospect that has galvanized both sides.

In an interview with the weekly L’Express magazine, President Sarkozy urged Mr. Netanyahu to “take the risk of peace.”

“In all my political life I have been a friend of Israel,” Mr. Sarkozy said. “But there will be no security for Israel without a viable, democratic and modern Palestinian state.”

Turning to the question of a possible declaration of Palestinian statehood in September, Mr. Sarkozy said that, if peace talks did not resume over the summer, “France will assume its responsibilities on the central question of recognizing the Palestinian state.”

In Berlin, Mrs. Merkel is skeptical about the Palestinian unity deal because Hamas does not recognize the right of Israel to exist and has not renounced terrorism.

The Central Council of Jews in Germany warned the government in Berlin on Thursday that the Palestinian unity meant that it was “not possible for Hamas to be a peace partner for Israel,” according to Dieter Graumann, the council’s president, speaking on German radio.

But Germany’s opposition Social Democrats said the unity agreement between Fatah and Hamas should be welcomed by the government.

“The overcoming of the divisions in the Palestinian society is a prerequisite for a successful peace process with Israel,” said Rolf Mützenich, a Social Democrat lawmaker and foreign affairs spokesman.

Despite Mrs. Merkel’s criticism of the unity accord, she has been outspoken about Israel’s continuing policy of building settlements in the West Bank. During talks in February and April with Mr. Netanyahu, she tried to persuade him to use the changes sweeping across the Middle East as a reason to restart the peace talks with the Palestinians.

But she has also said she will urge Mr. Abbas not to press for a United Nations declaration of statehood, according to German news reports. While Israel refuses to deal with Hamas, Mr. Abbas says the Palestinians cannot return to peace talks without a halt to all settlement activity by Israel.