  By means of the variational approximation (VA) and systematic simulations, we
study dynamics and stability boundaries for solitons in a two-dimensional (2D)
self-attracting Bose-Einstein condensate (BEC), trapped in an optical lattice
(OL) whose amplitude is subjected to the periodic time modulation (the
modulation frequency, $\omega $, may be in the range of several KHz). Regions
of stability of the solitons against the collapse and decay are identified in
the space of the model's parameters. A noteworthy result is that the stability
limit may reach the largest (100%) modulation depth, and the collapse threshold
may exceed its classical value in the static lattice (which corresponds to the
norm of Townes soliton). Minimum norm $% N_{\min}$ necessary for the stability
of the solitons is identified too. It features a strong dependence on $\omega $
at a low frequencies, due to a resonant decay of the soliton. Predictions of
the VA are reasonably close to results of the simulations. In particular, the
VA helps to understand salient resonant features in the shape of the stability
boundaries observed with the variation of $\omega $.
