Public safety agencies are using Land Mobile Radio in the Disaster environment for their communication. It is very crucial for the emergency communication between disaster responder and disaster commander due to the less data rates, less services and less multimedia services. Commercial cellular network provides higher data rates, higher service availability and more multimedia services. The Land Mobile Radio mobile node can be used the cellular network enhanced services, when it handoff to cellular network. The Existing Session Initiation Protocol(SIP) and Seamless Session Initiation Protocol improved the radio resource utilization with the constraint of handoff delay for enhancing the interoperability between LMR and cellular network. The proposed Network Resource Allocator request the Admission Bandwidth Adjustment for improving the radio resource utilization with the constraint of handoff delay and packet loss. In addition, the proposed method provides guarantee service availability and continuity of service for disaster responder and disaster commander communication. The Effectiveness of proposed scheme is illustrated by simulation results.