  We present a next-to-leading order computation in QCD of one-jet and two-jet
cross sections in polarized hadronic collisions. Our results are obtained in
the framework of a general formalism that deals with soft and collinear
singularities using the subtraction method. We construct a Monte Carlo program
that generates events at the partonic level. We use this code to give
phenomenological predictions for $pp$ collisions at $\sqrt{S}=500$ GeV,
relevant for the spin physics program at RHIC. The possibility of using jet
data to constrain the poorly known polarized parton densities is examined.
