GAZA, Aug 20 (Reuters) - Forty families whose houses were destroyed in conflict with Israel took over a building belonging to Gaza's Hamas rulers this week in a sign of dissatisfaction with the Islamist movement's failure to provide shelter.

Angered by living in tents for two winters and now baking in the midst of an intense heat wave, the squatters took over the unfinished apartment house and have already resisted one police effort to evict them.

The heat and cold hurt our children. Where are you? read a banner pasted on the wall of the building, in the first overt move against government property since Hamas seized power strip in 2007, ousting forces loyal to the Fatah movement of Palestinian President Mahmoud Abbas.

Bassam Jamil, one of the squatters, said 43 families had moved into the building which was still under construction in Jabalya in the northern Gaza Strip. It belongs to the Hamas-run housing ministry.

We have lost faith that anyone will rebuild our homes. We have taken shelter in the building from the heat in the tents we've been living in, Jamil said.

Thousands of homes and factories were destroyed by Israeli bombing and shelling in a 3-week offensive in Dec-Jan 2008-09 against Hamas militants, to stop them firing rockets at Israeli towns close to the Gaza Strip.

International donors pledged nearly $5 billion in reconstruction aid but no money has arrived, partly because of the feud between Hamas and Fatah. Israel's blockade of the territory also restricts supplies of cement and steel, which it says could be used for military purposes by Hamas.

Earlier this week, Hamas police tried to evict the families but were confronted with resistance by women and children.

The building has 44 unfinished apartments. The squatters say they are still better than tents. They have fitted their own doors and are now asking city authorities to turn on electricity and water.