03-20U

The quantum model of the system of relativistic nucleons with direct interaction has been built. Such a model is an alternative to the $\sigma $--model of quantum hadrodynamics and to the method of modelling potentials. By means of equation of state of nuclear matter the "liquid--gas" phase transition is studied in the case of $\beta $--stability, and the parameters of the critical point are found. It is shown that the presence of the phase transition is connected with relativistic effects. The model of isotropic neutron star is considered with the use of Oppenheimer--Volkoff equations. The obtained dependence of the star mass on its radius corresponds to the small neutron stars and differs from the standard one.