  Light transport in a disordered ensemble of resonant atoms placed in a
waveguide is found to be very sensitive to the sizes of cross section of a
waveguide. Based on self-consistent quantum microscopic model treating atoms as
coherent radiating dipoles, we have shown that the nature of radiation transfer
changes from Anderson localization regime in a single-mode waveguide to a
traditional diffuse transfer in a multi-mode one. Moreover, the transmittance
magnitude undergoes complex step-like dependence on the transverse sizes of a
waveguide.
