  The aspect of the quasiparticle interaction of a local Fermi liquid, the
impurity version of f$^2$-based heavy fermions, is studied by the Wilson
numerical renormalization group method. In particular, the case of the
f$^2$-singlet crystalline-electric-field ground state is investigated assuming
the case of UPt$_3$ with the hexagonal symmetry. It is found that the
interorbital interaction becomes larger than the intraorbital one in contrast
to the case of the bare Coulomb interaction for the parameters relevant to
UPt$_3$. This result offers us a basis to construct a microscopic theory of the
superconductivity of UPt$_3$ where the interorbital interactions are expected
to play important roles.
