An apparatus and method are provided for load balancing in a broadband communication system. In an initial network entry/network reentry/handover, whether to allow a user terminal and whether to allow each service flow are checked. The channel state and load state of candidate frequency assignments and subcells are detected. The ranging status of a corresponding frequency assignment or a corresponding subcell is set according to whether to allow the user terminal. The allowable candidate frequency assignment and subcells are selected and transmitted.