  The paper is devoted to the development of a microscopic description of the
critical behavior of a cell fluid model with allowance for the contributions
from collective variables with nonzero values of the wave vector. The
mathematical description is performed in the supercritical temperature range
($T>T_c$) in the case of a modified Morse potential with additional repulsive
interaction. The method, developed here for constructing the equation of state
of the system by using the Gaussian distribution of the order parameter
fluctuations, is valid beyond the immediate vicinity of the critical point for
a wide range of density and temperature. The pressure of the system as a
function of chemical potential and density is plotted for various fixed values
of the relative temperature, both with and without considering the
above-mentioned contributions. Compared with the results of the zero-mode
approximation, the insignificant role of these contributions is indicated for
temperatures $T>T_c$. At $T<T_c$, they are more significant.
