JERUSALEM — The emir of Qatar on Tuesday became the first head of state to visit the Gaza Strip since Hamas took full control of it in 2007, the latest step in an ambitious campaign by the tiny Persian Gulf nation to leverage its outsize pocketbook in support of Islamists across the region — and one that threatened to widen the rift between rival Palestinian factions.

The emir, Sheik Hamad bin Khalifa al-Thani, pledged $400 million to build two housing complexes, rehabilitate three main roads and create a prosthetic center, among other projects, a transformational infusion of cash at a time when foreign aid to the Palestinian territories has been in free fall. The sheik, his wife and the Qatari prime minister led a large delegation that entered Gaza from Egypt and sped in a convoy of black Mercedes-Benzes and armored Toyotas through streets lined with people waving Qatari and Palestinian flags.

“Today you are a big guest, great guest, declaring officially the breaking of the political and economic siege that was imposed on Gaza,” Ismail Haniya, the Hamas prime minister, told the emir and his cohort as they sat on sofas in a white shed in the southern town of Khan Yunis, where they plan to erect 1,000 apartments. “Today, we declare the victory on this siege through this blessed, historic visit.”

In the West Bank, allies of Mahmoud Abbas, the president of the Palestinian Authority, who has struggled to preserve his own legitimacy, warned that the visit set a dangerous precedent of Arab leaders’ embracing Mr. Haniya as a head of state and thus cleaving the Palestinian people and territory in two. “We call on the Qatari prince or his representative to visit the West Bank too!” blared a headline on an editorial in the leading newspaper Al Quds.

The visit signaled just how much the region had changed for Hamas since the advent of the Arab Spring. Where Egypt under President Hosni Mubarak once allied with Saudi Arabia to squeeze Hamas by keeping the border largely closed, Egypt under a new Islamist president, Mohamed Morsi, opened the crossing to allow the Qatari ruler through. But the visit also reflected the unique foreign policy that has allowed Qatar to straddle competing worlds, bankrolling political movements like Hamas, deemed a terrorist organization by the United States, while maintaining strong links to Washington.

Sheik Hamad, who has ruled Qatar since 1995, has gradually transformed the tiny nation into a regional powerhouse, relying on its immense wealth to extend its influence. That has been especially true in the past two years, as Qatar has played decisive roles in the revolutions in Libya and Yemen and the isolation of the Syrian government.

Qatar allied with the West in helping oust Col. Muammar el-Qaddafi in Libya, while financing Islamists on the ground. In Egypt, it has close ties to the Muslim Brotherhood. In Syria, it provides cash and weapons to Islamists battling President Bashar al-Assad, and at the same time it hosts a large United States military base that affords it protection in a volatile neighborhood.

“Qatar is a secure little kernel with huge resources that has chosen to use those resources in foreign policy,” said Paul Salem, director of the Beirut-based Carnegie Middle East Center. “They have no constraints. They can take any position anytime anywhere.”

But eight months after Doha, the Qatari capital, hosted the signing of a reconciliation agreement between the Hamas leadership and Mr. Abbas, the deal has not come to fruition in the form of national elections. On Tuesday the emir’s visit drove a deeper wedge between Hamas and Fatah, the party of Mr. Abbas, and raised alarm in Israel.

Hamas has refused to reject violence or recognize Israel, which also considers it a terrorist organization, and has struggled lately to control more militant Islamist groups within Gaza. Since the uprising began in Syria in March 2011, Hamas has closed its offices in Syria, its primary patron, and tried to establish a close and direct connection to Mr. Morsi of Egypt, who was a leader within the Muslim Brotherhood before his election.

Yigal Palmor, a spokesman for Israel’s Foreign Ministry, declared that the emir had “thrown peace under the bus,” noting that his visit came a few hours after an Israeli soldier was severely wounded when a bomb exploded along the border with Gaza. Southern Israel has faced what he described as “a steady drizzle of rockets” in the last few weeks.

“It helps Hamas entrench themselves in Gaza, not to yield one inch to the P.A., and enhancing the division and the reality of two de facto states,” Mr. Palmor said. “Most of the money that he’s pouring in Gaza will go to Hamas pockets, directly or indirectly. You think that will encourage them to hold national elections?”

The Qatari projects dwarf the roughly $300 million in foreign aid that analysts estimate Gaza receives annually. They come as international donations to the Palestinian Authority have nose-dived, from a peak of $1.8 billion in 2008 to less than $700 million this year, according to a World Bank report. The shift is part of a broader financial crisis that has caused the delayed or partial payment of government salaries three months running, the focus of violent street protests in the West Bank last month.

Nathan Thrall, an analyst with the International Crisis Group, said a critical question was whether rumored visits to Gaza by other regional heads of state would follow Qatar’s. He said that Cairo’s role in brokering the visit was an important signal in the evolving relationship between Gaza and Egypt, and that Hamas was hoping it would help reverse the so-called “West Bank-first model of attempting to promote prosperity in Ramallah and austerity in Gaza.”

“The message that Hamas wishes to convey is ‘We are the future; the P.A. is disintegrating,’ ” he said. “The argument Hamas is hoping to make is that this is the beginning of a sort of Gaza-first model: Arabs ignoring a failing P.A., and supporting Gaza with sums of money that Europeans, even if they wanted to, couldn’t match.”

The six-hour visit ended with a large rally at the Islamic University in Gaza City, where the emir and his wife received honorary doctorates.

Speaking at the university, he called on Palestinian leaders to repair their rift, which he said “was more painful than the Israeli aggression” and left them “without peace negotiations or a resistance and liberation strategy.”