Localization of electrons at dielectric-metal interfaces is studied in the framework of a continuum model. The layer of thickness L, with a negative electron affinity, is characterized by the static dielectric constant epsilons and by the optical dielectric constant epsiloninfinity. It is found that the electron localization along the plane of the interface occurs if the layer thickness exceeds a critical value Lc. In the case of a high polar layer, the electron energy of the localized ground state shows a nonmonotonic dependence on the layer thickness. A strong correlation between low-lying excitations and the spread of the localized state has been established. The magnitude of the correlation parameter is close to the analogous correlation for the solvated electron in the bulk. The localization dynamics is discussed in terms of relaxation along a polarization coordinate, which is directly connected to the polarization energy of the layer.