The process of optical anisotropy indiction in azopolymer films upon irradiation by polarized UV light is studied by means of UV and IR birefringence spectroscopy. A substantial dependence of the character of the relaxation of the induced anisotropy on the exposure time to the exciting light is revealed: whereas the process of anisotropy induction is reversible at small exposure times, at large exposure times the induced anisotropy virtually does not relax and even increases after the irradiation is terminated. A difference between kinetic curves of dichroism and birefringence induction is shown: at exposure times corresponding to the saturation of the induced dichroism a slow increase in the birefringence curve is observed. Results obtained are explained in terms of the assumption of partial ordering of macrochain fragments in irradiated films. The assumption is substantiated by measurements of polarized IR spectra.