This paper contributes a new adaptive approach to prevent handoff failure due to lack of resources in adjacent cells in a mobile cellular network. Known as the Measurement-based Pre-assignment (MPr) technique, the technique is useful for implementation in micro/pico cellular networks which offers a Quality of Service (QoS) guarantee against call dropping. The technique is fully automated, simple, efficient, robust and generic for implementation. The notable feature is that the technique accepts different QoS specifications for different grades of handoff calls and ensures that these QoS levels are preserved under changing load conditions.