A pseudopotential model for the description of binding of an excess electron to polar clusters or molecules is presented. In addition to Coulomb, short range repulsion, and polarization interactions between the excess electron and the neutral core, the model also accounts for dispersion within a second order perturbation treatment. The pseudopotential, which should enable future dynamical calculations coupling the excess electron with nuclear motions, is successfully tested against accurate ab initio results for a whole set of geometries of hydrogen fluoride dimer anion. Predictions are made for an electron bound to a collinear hydrogen fluoride trimer for different values of the intermonomer separations. For the optimal and shorter values of this separation two bound states of the excess electron in (HF)(3)(-) are predicted to exist.