Mohammed Irhaiem's former home was a spacious 1,500 square feet and was built from solid concrete blocks. It had views of the Mediterranean and fruit trees in the yard.

His new home, which he surveyed for the first time this week, measures 12 by 6 feet and is made of sheets of canvas held aloft by three wooden poles. His is one of 90 bright white tents that have sprouted in neat rows amid a sea of gray rubble, the wreckage from homes -- including Irhaiem's -- that were destroyed during the 22-day Gaza war between Israel and Hamas.

"It's humiliating," said Irhaiem, 49, clutching the hand of his barefoot young grandson as he contemplated life for himself and 24 relatives in the tent colony.

But it will have to do: Three weeks after the war's end, the reconstruction of the Gaza Strip has scarcely started, caught in a web of political battles that aid workers worry could prevent the work from ever getting done.

The most daunting obstacle is the lack of construction supplies, which are badly needed to rebuild the approximately 4,000 homes that were destroyed in the fighting and repair an additional 17,000 that were damaged. The United Nations estimates that as many as 100,000 people were rendered homeless by the war.

But Israel has banned raw materials from entering Gaza, reasoning that goods such as cement and steel could be used by Hamas to build bunkers or manufacture rockets.

Beyond the security concerns, Israeli officials say they are determined not to let Hamas gain politically by overseeing the reconstruction.

Hamas, meanwhile, appears just as determined to turn the reconstruction to its advantage. The group, which has controlled Gaza for the past year and a half, has insisted that it be allowed to coordinate all rebuilding work. It has also made clear that its chief Palestinian rival, the moderate Fatah party, will not be welcome during the recovery, despite Israeli and U.S. wishes that Palestinian Authority President Mahmoud Abbas, a Fatah member, be given a lead role.

Last week, Hamas police seized 3,500 blankets and 400 food packages from a U.N.-affiliated warehouse because Hamas said the goods were being distributed in Abbas's name. The United Nations denied the charge and suspended aid shipments Friday in protest after Hamas allegedly confiscated additional aid supplies from 10 trucks.

Hamas has distributed its own aid to those affected by the war, giving thousands of dollars to each family that lost a home or a loved one. But with no building materials, it has been unable to launch the sort of large-scale reconstruction effort that the Lebanese militia Hezbollah undertook after its 2006 war with Israel.

The battles over reconstruction -- between Israel and Hamas and between Hamas and Fatah -- underscore the degree to which everything in Gaza, humanitarian efforts included, has become politicized.

Hamas has controlled Gaza since June 2007, when it routed Fatah loyalists. Gaza, a narrow coastal territory that is home to 1.5 million Palestinians, has been kept under a tight Israeli embargo ever since, decimating the economy.

War broke out in late December, as Israel launched a surprise attack that it said was aimed at halting Hamas rocket fire from the strip. The war, which ended with a tenuous cease-fire, left approximately 1,300 Palestinians dead, about half of them civilians, according to Gazan health officials. Thirteen Israelis died in the fighting, three of them civilians.

Hamas economics minister Ziyad al-Zaza asserted in an interview in his Gaza City office that Abbas and Israel worked together during the war and continue to do so, attempting to use the reconstruction to weaken Hamas.

"Mahmoud Abbas couldn't get into Gaza on the back of an Israeli tank. So now they're trying to get him in through the aid he's offering," Zaza said. "It's unacceptable."

John Ging, head of the U.N. Relief and Works Agency in Gaza, said the seizure of aid last week marked the first time since Hamas came to power that the Islamist movement had interfered with his organization's work.

But it may not be an isolated incident. Hamas's desire to orchestrate the reconstruction has led it to crack down on Fatah-affiliated charities in recent weeks, according to members of those groups. One group had its supplies confiscated and was threatened by Hamas police officers three times, according to Mohammed, a director of the organization who would not allow his last name to be made public for fear of retribution.

"They treated me like a collaborator," Mohammed said as he nervously smoked a cigarette. "They're trying to show people that they're still in control. And they want to make sure the supplies are only distributed to the people who support them."

Mohammed spoke in a nearly empty room decorated with children's artwork and colorful streamers. Normally, he said, the group hosts an after-school program for 60 children and distributes food and clothing to needy families, regardless of their political affiliation. But since the war ended, he said, Hamas threats had forced the group to stop its work at a time when it is most acutely needed.

Israel cites such incidents in justifying its strict limits on the types of goods that can enter the strip. "Hamas is stealing food supplies. What are they going to do with raw materials?" said Maj. Peter Lerner, an Israel Defense Forces spokesman. In the past, Lerner said, Hamas has used pipes intended for a sewage treatment plant to make rockets.

But the ban on raw materials extends to goods that have no apparent military application. Paper, for instance, is prohibited.

Ging, the U.N. official, said the paper shortage has kept textbooks out of the hands of students, further disrupting a semester that had already been delayed by war.

"We're ready at a moment's notice to commence construction, just as soon as we can get construction material into Gaza," Ging said. "But I have no confidence that will happen if I can't even get paper to educate the children."

The United Nations has called for $613 million in emergency relief funds for Gaza, part of a recovery effort estimated to cost $2 billion or more. During a visit to Jerusalem late last month, George J. Mitchell, the U.S. special envoy for the Middle East, announced that Americans would give an additional $20 million in aid to Gaza. He also called for Israel to open the border crossings.

The crossings are at the heart of negotiations, mediated by Egypt, for a more lasting truce. Hamas has demanded that the crossings be opened. But Israel has balked, pushing for Hamas to first release captured Israeli Cpl. Gilad Shalit. Shalit has been held by Hamas in Gaza since 2006. Israel is also seeking a complete end to rocket fire from the strip; since the cease-fire, there have been sporadic attacks, which Israel has countered with periodic airstrikes.

As the talks drag on, Palestinians in Gaza say they are losing hope that their lives will be rebuilt. For the Abed Rabbo family, that means staying indefinitely in the wreckage of what was once an imposing four-story home.

During the Israeli assault, the home was struck by shells and collapsed. The cracked ceilings now rest at 45-degree angles to the floors. The exterior walls are gone. Chunks of cement and twisted iron rods seemingly lie everywhere, but members of the extended family of 40 have carved out small bits of space where they can cook, eat and sleep.

"The engineers say it's dangerous to stay here. But where else can I go? All my relatives lost their homes, too," said Mohammed Abed Rabbo, a 55-year-old who walks with a pronounced limp from various injuries sustained during previous fighting and who once worked as a mechanic in Israel.

"I spilled my blood in this home. I'm not leaving it."