A microscopic theory of a solvated electron in simple polar liquid is presented. The Pekar-Frohlich variational approach is extended to account for the finite size of the solvent molecules, The solvated electron is assumed to be completely localized within the cavity created in the solvent. The total energy of the localized electron in the solvent of polarizable hard spheres is derived within the framework of the mean-spherical approximation (MSA). The effect of the molecular size of the solvent, its polarity and polarizability on the equilibrium properties of the solvated electron, namely the radius of the cavity and the binding energy, is studied, Results for the hydrated electron are in a good agreement with the numerical simulations, (C) 1997 American Institute of Physics.