A macroscopic model for calculating potential energy for nuclear shapes relevant in fusion and fission processes is presented. The potential energy is calculated as the sum of the Yukawa-plus-exponential folding potential and the Coulomb energy assuming realistic, diffuse charge distributions. Shape independent components (e.g. the Coulomb exchange and Wigner terms) in the Krappe--Nix--Sierk formulae for the total energy were combined and adjusted to the experimental ground state masses of the compound nucleus (for the mononuclear regime), and two separated nuclei (for the binary regime), and assumed to change in the transition region between these two regimes. We have used experimental data on heights of the saddle point (experimental fission barriers) and the interaction barrier (experimentally deduced fusion barriers) to verify our model calculations. Very good agreement with the fission barrier data proved correctness of our description of the shell-correction energies. Predictions of the interaction barriers also agree very well with experimental data. The calculated interaction barriers are significantly lower than those predicted with the ``proximity potential'', and agree with the experimentally deduced fusion barriers.

PACS numbers: 25.85.--w, 25.70.Jj