97-30U

The collective variables method with a reference system is applied to the study of the binary "symmetrical" mixture behaviour in the vicinity of the gas-liquid critical point. The basic density measure (model $\rho^4$) is constructed in $\rho_{\vec k}$- variable phase space which contains the variable $\rho_0$ connected with the order parameter of the system. The corrections $\Delta {\cal M}_n$ to the basic cumulants in the transition Jacobian arising after integration over unessential collective variables are calculated. It is shown that the problem can be reduced to the calculation of the grand statistical sum functional of 3D Ising model in an external field.