Projector on physical states in loop quantum gravity

We construct the operator that projects on the physical states in loop quantum gravity. To this aim, we consider a diffeomorphism-invariant functional integral over scalar functions. The construction defines a covariant, Feynman-like, spacetime formalism for quantum gravity and relates this theory to the spin foam models. We also discuss how expectation values of the physical quantity can be computed. [S0556-2821(99)04210-1].