  It is commonly accepted that the peak effect (PE) in the critical current
density of type II superconductors is a consequence of an order-disorder
transition in the vortex lattice (VL). Examination of vortex lattice
configurations (VLCs) in its vicinity requires the use of experimental
techniques that exclude current induced VL reorganization. By means of linear
ac susceptibility experiments in the Campbell regime, where vortices are forced
to oscillate (harmonically) around their effective pinning potentials, we
explore quasi-static stable and metastable VLCs in NbSe_{2} single crystals
near the PE. We identify three different regions: for T<T_{1}(H), stable VLCs
are maximally ordered. For T>T_{2}(H) configurations are fully disordered and
no metastability is observed. In the T_{1}<T<T_{2} region we find temperature
dependent stable configurations with intermediate degree of disorder, possibly
associated to coexistence of ordered and disordered lattices throughout the PE.
A simple estimation of the equilibrium proportion of ordered and disordered
domains is provided.
