  This paper proposes a definition of gravitational observables and of their
path integral formula within the framework of ADM foliation and the choice of
unimodular gauge classes. The method enforces a BRST invariant gauge fixing of
the lapse and shift fields. It yields the quantum level extension of the known
classical property that the conformal classes of internal metrics of constant
Lorentz time leafs define the gravitational physical degrees of freedom.
