  For a fast particle moving within a two-dimensional array of soft scatterers
- centers of weak and short-range potential - the dependence of the Lyapunov
exponent on the system parameters is studied. The use of the linearized
equations for variations of the propagation angles and impact parameters of
consequent collisions reduces the problem to that of calculation of the
Lyapunov exponent of an ensemble of strongly correlated random matrices with
given statistics of matrix elements. In the simplest approximation this
Lyapunov exponent is proportional to the interaction strength and inversely
proportional to the square root of the interaction range. The model
satisfactorily describes the intensity of chaos in a system of two weakly
interacting particles moving in a two-dimensional regular confining potential.
