  General formulas are derived for the quasiparticle effective mass and the
equation of state of the Fermi system with account of the interparticle
attraction at long distances and repulsion at short distances. Calculations are
carried out of the equation of state and the effective mass of the Fermi system
at zero temperature with the use of the modified Morse potential. It is shown
that the pair repulsive forces promote a decrease of the effective mass, and
the attractive forces promote its increase. With a certain choice of the
parameters of the potential the dependence of the pressure on the density has a
nonmonotonic character, which enables to describe the coexistence of the liquid
and gaseous phases. The influence of three-body interactions on the equation of
state and the effective mass is considered. The calculation results are
compared with experimental data concerning the quasiparticle effective mass in
the liquid $^3$He.
  Key words: normal Fermi liquid, effective mass, quasiparticle, equation of
state, interaction potential
