After the deregulation of the Power Sector in the U.S., planning for generation and transmission capacities is decentralized. There is, however, still need for the long term integrated planning of generation and transmission capacities at the macro level, since these two sectors must operate in a coordinated manner. This paper presents a model for integrating generation and transmission expansion planning to identify an indicative expansion plan for the total sector at the macro level. The argument for an integrated model is supported using evidence from integrated planning efforts in real life systems. The application of the proposed model is illustrated using an example that requires expansion of generation and transmission capacities over three regions in a deregulated power system. The example considers that addition of generating capacity should come from renewable sources. The test results show the potential cost saving from integrated planning.