  The classical field equations of general relativity can be expressed as a
single geodesic equation, describing the free fall of a point particle in
superspace. Based on this formulation, a ``worldline'' quantization of gravity,
analogous to the Feynman-Schwinger treatment of particle propagation, is
proposed, and a hidden mass-shell parameter is identified. We consider the
effective action for the supermetric, which would be induced at one loop. In
certain minisuperspace models, we find that this effective action is stationary
for vanishing cosmological constant.
