  Emergent model spectra of neutron star atmospheres are widely used to fit the
observed soft X-ray spectra of different types of isolated neutron stars. We
investigate the effect of Compton scattering on the emergent spectra of hot
(T_eff > 10^6 K) isolated neutron stars with weak magnetic fields. In order to
compute model atmospheres in hydrostatic and radiative equilibrium we solve the
radiation transfer equation with the Kompaneets operator. We calculate a set of
models with effective temperatures in the range 1 - 5 * 10^6 K, with two values
of surface gravity (log g = 13.9 and 14.3) and different chemical compositions.
Radiation spectra computed with Compton scattering are softer than those
computed without Compton scattering at high energies (E > 5 keV) for light
elements (H or He) model atmospheres. The Compton effect is more significant in
H model atmospheres and models with low surface gravity. The emergent spectra
of the hottest (T_eff > 3 * 10^6 K) model atmospheres can be described by
diluted blackbody spectra with hardness factors ~ 1.6 - 1.9. Compton scattering
is less important in models with solar abundance of heavy elements.
