That's incorrect. The Palestinian Authority is run by Fatah, which is rivals with Hamas (and, in fact, is engaged in a civil war with Hamas). The PA controls the West Bank, Hamas controls Gaza.
Fatah and Hamas signed a reconciliation deal in May of 2011 and it is being worked out now to implement it. A national unity agreement with elections to follow is the result. It would be extremely naive to believe that U.S. aid would not reach Hamas. Even more so to believe that Hamas is sincere on its pledge to renounce violence.
I wonder how much authority the Palestinian Authority really has without Hamas? Very little, I suspect. That’s why giving money to the PA is so dangerous. There is even rumors that Hamas will be taking over the PA.