Similar to a mobile-user in the cell-based GSM, a satellite in a LEO system constantly circulates along its predesigned orbit. Satellites' movement causes their visibility change, and thus a user's call needs to be handed over among satellites from time to time. The handovers may occur frequently. Without handling those calls well, the system performance will degrade. This paper dealt with call admission control and considered a multiservice LEO system allocating various bandwidths for different calls (so-called multirate). A novel guard-channel policy that reserves appropriate channels for various types of handover calls was proposed. It applied SMDP theory to find optimal channel reservation, on the premise of CoS guarantee to handover calls. The results manifested that under various traffic conditions, this SMDP-based guard-channel policy performed better than coordinate-convex and ordinary SMDP-based policies.