The analytical and numerical study of the radiation self-action in a system of coupled light guides is fulfilled on the basis of discrete nonlinear Schr?dinger equation (DNSE). We develop a variational method for qualitative study of DNSE and make classification of self-action modes. We show that the diffraction of narrow (in grating scale) wave beams weakens in discrete media and, consequently, the ``collapse'' of one-dimensional wave field with power exceeding the critical value appears. This results in the ability to self-channeling radiation in the central fiber. Qualitative analytical results were confirmed by numerical simulation of DNSE, which also show the stability of the collapse mode.