The purpose of urban planning gaming is to make experiments in decision-making for urban plans. In order to produce satisfactory results of training in gamings, it is necessary to develop computer assisted gaming support systems. In this paper, firstly, we propose a project planning system as one of gaming support systems which interactively assists players to make their action programs by coordinating them in project programs which compose an urban plan. Secondly, we present the logical foundation on design of project planning systems, which is an assumption-based temporal reasoning method named ASTRON. We describe the knowledge representation, the reasoning procedure of ASTRON and its application to project planning. Lastly we describe a trial implementation of project planning system named PASTERE which is built on the knowledge system building tool WORLDS.