The recent data from the H1 Collaboration on hadron multiplicity in diffractive DIS is studied in the framework of perturbative QCD as a function of invariant diffractive mass. The formulas obtained explain the observed excess of particle production in diffractive DIS relative to that in DIS and e(+)e(-) annihilation. It is shown that the results are sensitive to the quark-gluon structure of the Pomeron. Namely, the data are in favor of a superhard gluon distribution at the initial scale. [S0556-2821(99)02813-1].603