Corrections of order alpha(3)(s) to R(had) in pQCD with light gluinos

By a completely independent analytic calculation made in general covariant gauge we confirm the known result for the massless O(alpha(s)(3)) correction to R(had) and check explicitly its gauge independence. We extend the calculations to include contributions due to a hypothetical existence of a colour octet of (light) neutral fermions known also under the name of gluinos. In numerical form and for five active flavours we found (in MS scheme) that R(s) = 11/3[1 + alpha(s)/pi + (1.409 - 0.346ng)(alpha(s)/pi)(2) + (-12.805 - 3.006n((g) over tilde) - 0.0466n((g) over tilde)(2))(alpha(s)/pi)(3)] where n((g) over tilde) is the number of such colour octets. The gluino (alpha(s)(3)) contribution to the Z-boson hadronic decay rate proves to be relatively small while it is significant for tau-lepton semihadronic width.