  The non-abelian analog of the Landau-Pomeranchuk-Migdal effect is
investigated in perturbative QCD. Extending our previous studies, the
suppression of induced soft bremsstrahlung due to multiple scatterings of
quarks in the spinor representation is considered. The effective formation time
of gluon radiation due to the color interference is shown to depend on the
color representation of the emitting parton, and an improved formula for the
radiative energy loss is derived that interpolates between the factorization
and Bethe-Heitler limits.
