An evident form of the quantum generalization of the Gel'fand-Dikii formula [M. Gel'fand and L.A. Dikii, Russ. Math. Surv. 30, No. 5 (1975) 77; Funct. Anal. Appl. 10 (1976) 13; 11 (1977) 93] has been found as a development of the Lukyanov-Fateev approach to W-algebras. The necessity of ordering the quantum fields leads to the deformation of pseudodifferential symbols.