  We propose a nonlinear sigma model for the description of quantum transport
in a mesoscopic metallic conductor with magnetic impurities frozen in a spin
glass phase. It accounts for the presence of both the corresponding scalar and
magnetic random potentials. In a spin glass, this magnetic random potential is
correlated between different realizations. As the strength of the magnetic
potential is varied, this model describes the crossover between orthogonal and
unitary universality classes of the nonlinear sigma model. We apply this
technique to the calculations of the correlation of conductance between two
frozen spin configurations in terms of dephasing rates for the usual low energy
modes of weak localization theory.
