  We have generalized the scattering-matrix theory of multiple Andreev
reflections in mesoscopic Josephson junctions to the multi-mode case, and
applied it to short superconductor/normal metal/superconductor junctions with
diffusive electron transport. Both the dc and ac current-voltage
characteristics are analyzed for a wide range of bias voltages $V$. For
voltages smaller than the supeconducting gap the dc differential conductance of
the junction diverges as $1/\sqrt{V}$.
