  We develop a general method for calculating statistical properties of the
speckle pattern of coherent waves propagating in disordered media. In some
aspects this method is similar to the Boltzmann-Langevin approach for the
calculation of classical fluctuations. We apply the method to the case where
the incident wave experiences many small angle scattering events during
propagation, but the total angle change remains small. In many aspects our
results for this case are different from results previously known in the
literature. The correlation function of the wave intensity at two points
separated by a distance $r$, has a long range character. It decays as a power
of $r$ and changes sign. We also consider sensitivities of the speckles to
changes of external parameters, such as the wave frequency and the incidence
angle.
