Fatah and Hamas so far disagree on who should lead a unity government, a possible sign of discord before talks scheduled to start in Cairo on Tuesday, prompting Palestinian officials and analysts to question the durability of the recent reconciliation agreement.

The Egyptian-brokered pact was reached unexpectedly and signed formally at a ceremony in Cairo on May 4. It was meant to end four years of schism between the mainstream Fatah, the dominant party in the West Bank, and the Islamic militant group Hamas, which controls Gaza, and the subsequent division between the two territories.

Spurred by popular pressure for national unity and rattled by turmoil elsewhere in the region, the rival leaderships of the two territories pledged to resolve their differences. In addition, the Palestinian Authority president and Fatah chief, Mahmoud Abbas, has an interest in presenting at least a semblance of unity if the Palestinians move ahead with a plan to seek international recognition of statehood at the United Nations in September.

When it comes to working out the details of reconciliation, however, the sides seem to have become bogged down.

The first issue is the formation of an interim government of independent technocrats to be agreed upon by both factions. That government is meant to administer the Palestinian territories and pave the way for presidential and parliamentary elections within a year.

There has been little progress so far. This weekend the Fatah Central Committee, the party’s main decision-making body, endorsed Salam Fayyad, the current Palestinian Authority prime minister, as their top candidate to lead the interim government. An American-trained economist, Mr. Fayyad is an internationally accepted figure who has gained the confidence of the West.

But Hamas has already rejected Mr. Fayyad’s nomination, saying that the new prime minister should come from Gaza.

“For us, Fayyad is unacceptable because his name is connected with a black phase in the history of the Palestinian people,” said Taher al-Nounou, a Hamas official in Gaza, who blamed Mr. Fayyad for deepening the split, closing Hamas institutions in the West Bank and pursuing security cooperation with Israel.

Both Fatah and Hamas figures said they thought the issue would not be solved in this next round of talks. “There is no deadline,” said Muhammad Shtayyeh, a member of the Fatah Central Committee, speaking by phone from Ramallah in the West Bank. “We will try to finish things in this round, but I think it will take longer.”

Mr. Shtayyeh foresaw more problems in other appointments, like the minister of interior, who has responsibility for the security forces. He and others said these details would ultimately have to be resolved by Mr. Abbas and Khaled Meshal, the Damascus-based leader of Hamas.

Still, Palestinian analysts suggest that the problems may run much deeper.

“I am worried,” said Mahdi Abdul Hadi, director of the Palestinian Academic Society for the Study of International Affairs, an independent institute in East Jerusalem, and one of a group of independent Palestinians who encouraged the unity accord.

“It is not a question of appointing a prime minister, but of the political will to share power. I do not see it,” he said.

Hani Habib, an analyst based in Gaza, said: “I do not think there is a real reconciliation. There is an atmosphere of reconciliation.” But, he said, he sees “a series of obstacles and a lack of determination” on both sides.

Palestinian politics are fractious at the best of times, and there are also divisions within Fatah and Hamas. This weekend, the Fatah Central Committee expelled one of its members, Muhammad Dahlan, a former Fatah security chief who came from Gaza. The official Palestinian news agency, Wafa, said the committee had decided “to bring Dahlan to justice based on criminal, financial and other charges made by a Fatah investigative commission.”

Mr. Dahlan has long been despised by Hamas; more recently he fell afoul of Mr. Abbas.

The delay in actually forming a unity government, keeping the reconciliation on paper only, may also be convenient for Mr. Abbas. Israel has rejected any dealings with a government backed by Hamas, and the Obama administration has expressed strong reservations about the reconciliation accord. The formation of a unity government could cancel any chance of peace talks with Israel and jeopardize American aid to the Palestinian Authority.

But some Palestinians expected at least a facade of unity to last. “We cannot afford to fail,” said Mr. Shtayyeh, the Fatah official. “Palestinian unity is a crucial issue for our future. Without Gaza, there is no state.”

Egypt also remains a powerful player in the accord, and its interim government is likely to intervene to prevent a collapse of the deal, a prospect that may aid the Palestinians while aggravating tensions with Israel.

The two neighbors have long abided a cold peace. But with the fall of President Hosni Mubarak’s government, Egypt’s foreign policy has appealed more to the popular anti-Israel sentiment of the street, increasing tensions. Now, as the Hamas-Fatah talks play out, yet another development has emerged to heighten the tension: Egyptian authorities on Monday accused Ilan Grapel, an American-Israeli citizen in Egypt, of spying for Israel and ordered him held for 15 days.

A statement by Egypt’s public prosecutor said Mr. Grapel, first detained on Sunday, had been sent to Egypt to recruit agents. Egyptian officials have also accused him of incitement during the revolution and of trying to create strife between Egypt’s Muslims and Coptic Christians.

The Israeli newspaper Haaretz published an interview with Mr. Grapel in 2006 after he was wounded while fighting as an Israeli combat soldier in that summer’s war in Lebanon.

The Israeli Foreign Ministry said on Monday that Mr. Grapel had entered Egypt on his American passport and was therefore under the jurisdiction of the American Consulate in Egypt.

“He is certainly no spy or spook,” said Yigal Palmor, the spokesman for the Israeli Foreign Ministry. “Why he was picked by the Egyptian authorities is beyond us.”