A variational method is developed based on the Hartree-Fock approximation, but not restricted to a single Slater determinant trial space. The idea is to find a subspace of collective states which are strongly coupled to the ground state by providing a systematic technique to generate these basis states from a Hartree-Fock-like state. In the resulting basis space a residual diagonalization is easily performed. An application to a solvable model is made, both to justify and to investigate the structure of our approach.Facultad de Ciencias Exactas