  The self-action features of wave packets propagating in a two-dimensional
system of equidistantly arranged fibers are studied analytically and
numerically on the basis of the discrete nonlinear Schr\"odinger equation.
Self-consistent equations for the characteristic scales of a Gaussian wave
packet are derived on the basis of the variational approach, which are proved
numerically for powers $\mathcal{P} < 10 \mathcal{P}_\text{cr}$ exceeding
slightly the critical one for self-focusing. At higher powers, the wave beams
become filamented, and their amplitude is limited due to nonlinear breaking of
the interaction between neighbor light-guides. This make impossible to collect
a powerful wave beam into the single light-guide. The variational analysis show
the possibility of adiabatic self-compression of soliton-like laser pulses in
the process of their three-dimensional self-focusing to the central
light-guide. However, the further increase of the field amplitude during
self-compression leads to the longitudinal modulation instability development
and formation of a set of light bullets in the central fiber. In the regime of
hollow wave beams, filamentation instability becomes predominant. As a result,
it becomes possible to form a set of light bullets in optical fibers located on
the ring.
