The survey, published by the UN Development Program, said that much of the repair work that has been carried out has used materials smuggled in through tunnels from neighboring Egypt to circumvent Israeli and Egyptian blockades.
Constrained by those sanctions, the report said, traditional international aid donors find themselves severely handicapped.
"Many members of the international community, including the United Nations, have refrained, thus far, from utilizing materials identified as coming through the tunnels, subsequently limiting their role in reconstruction," it said.
"While some recovery is taking place, the realities on the ground show that the international community is, by and large, rendered ineffective in addressing the needs of people in Gaza."
The United Nations says that at least 6,268 homes in the densely populated and impoverished Palestinian enclave were destroyed or severely damaged during the fighting between December 27, 2008 and January 18, 2009.
About 1,400 Palestinians were killed in the conflict and 13 Israelis died in combat or from militant rocket attacks on Israel.
Gaza's 1.5 million people have largely relied on a web of tunnels beneath the border with Egypt since Israel and Egypt tightened frontier controls after the militant Islamist group Hamas seized power there in June 2007.
The World Bank estimates that 80% of Gaza's imports arrive by tunnel.
Most of the tunnels are used to bring in basic goods such as food, household appliances, building materials and livestock, but Hamas and other armed groups use their own more secret tunnels to smuggle in weapons and money.
Further $527 million needed
The UN report examines reconstruction carried out between the end of the 23-day Israeli campaign in January 2009 and January 2010. During that period, it said, only 25% of the damage was repaired, much of it by local recycling of rubble and debris.
It said that by targeting emergency repair and reconstruction of homes and agricultural infrastructure, Arab and Islamic organizations had been more effective in helping than Western international agencies, which were hampered by the Israeli embargo on materials.
As examples, the report cites groups such as Islamic Relief, Qatar Red Crescent, Qatar Charity, Human Appeal International, Al-Rahma Charity Association, Mercy Malaysia and Muslim Hands.
The report said that while more than $173 million (137 million euros) was spent on repairs in 2009, a further $527 million was needed just to return the strip to its physical state prior to the Israeli offensive.
"In view of the scale of the needs, international assistance in Gaza is tantamount to tinkering at the edges," it said.