  We extract diffractive parton densities from data on diffractive deep
inelastic scattering (DIS) and on diffractive photoproduction of jets. We
explore the results of several ansaetze for the functional form of the parton
densities. Then we use the fitted parton densities to predict the diffractive
production of jets and of W's and Z's in p-pbar collisions at the Tevatron. To
fit the photoproduction data requires a large gluon density in the Pomeron. The
predictions for the Tevatron cross sections are substantially higher than data;
this signals a breakdown of hard-scattering factorization in diffractive
hadron-hadron collisions.
