Polygonal Models are ubiquitous in Computer Graphics but their real time manipulation and rendering especially in interactive application environments have become a threat because of their huge sizes and complexity. A whole family of automatic algorithms emerged during the last decade to help out this problem, but they reduce the complexity of the models uniformly without caring about semantic importance of localized parts of a mesh. Only a few algorithms deal with adaptive simplification of polygonal models. We propose a new model for user-driven simplification exploiting the simplification hierarchy and hypertriangulation model  that lends a user the most of the functionalities of existing adaptive simplification algorithms in one place and is quite simple to implement. The proposed new underlying data structures are compact and support real time navigation across continuous LODs of a model; any desirable LOD can be extracted efficiently and can further be fine-tuned. The proposed model for adaptive simplification supports two key operations for selective refinement and selective simplification; their effect has been shown on various polygonal models. Comparison with related work shows that the proposed model provides combined environment at reduced overhead of memory space usage and faster running times.