  A detailed description of the method for analytical evaluation of the
three-loop contributions to renormalization group functions is presented. This
method is employed to calculate the charge renormalization function and
anomalous dimensions for non-Abelian gauge theories with fermions in the
three-loop approximation. A three-loop expression for the effective charge of
QCD is given. Charge renormalization effects in the SU(4)-supersymmetric gauge
model is shown to vanish at this level. A complete list of required formulas is
given in Appendix.
  The above-mentioned results of three-loop calculations have been published by
the present authors (with A.Yu., Zharkov and L.V., Avdeev) in 1980 in Physics
Letters B. The present text, which treats the subject in more details and
contains a lot of calculational techniques, has also been published in 1980 as
the JINR Communication E2-80-483.
