  Dimensional reductions of various higher dimensional (super)gravity theories
lead to effectively two-dimensional field theories described by gravity coupled
G/H nonlinear sigma-models. We show that a new set of complexified variables
can be introduced when G/H is a Hermitian symmetric space. This generalizes an
earlier construction that grew out of the Ashtekar formulation of two Killing
vector reduced pure 4d general relativity. Apart from giving some new insights
into dimensional reductions of higher dimensional (super)gravity theories,
these Ashtekar-type variables offer several technical advantages in the context
of the exact quantization of these models. As an application, an infinite set
of conserved charges is constructed. Our results might serve as a starting
point for probing the quantum equivalence of the Ashtekar and the metric
formalism within a non-trivial midi-superspace model of quantum gravity.
