Recently, there has been great interest in the integration of Distributed Energy Resources (DER) at the distribution level. DERs are potentially valuable providers of ancillary services such as load following and contingency reserve in distribution systems. This will require new control strategies for coordinating their system performance. One issue that has not been addressed sufficiently is the coordinated dispatch of large numbers of DERs under normal operation or system outage. In this paper, an AGC type control strategy is proposed and implemented for the real time control of DERs. Simulation results show that DERs are capable of providing load following and contingency reserve services under the proportional control mode or competitive control mode.