The program was launched with high expectations at an international conference in Cairo on Oct. 12, but has run into obstacles, including wrangling between the rival Palestinian factions Hamas and Fatah for control in Gaza and what officials say has been a trickle of promised aid. Hardest hit by delays are tens of thousands of Gazans living in communal shelters or the ruins of their homes since the summer war between Israel and the Islamic militant Hamas destroyed or damaged some 100,000 homes. The United Nations, in turn, devised a system under which Israel would gradually ease a ban on selling building materials to Gaza, with U.N.