  Two-loop evolutions of the gauge couplings in a class of intermediate scale
supersymmetric SO(10) models including the effect of third generation Yukawa
couplings are studied. The unification scale, the intermediate scale and the
value of the unification gauge coupling in these models are calculated and the
gauge boson mediated proton decay rates are estimated. In some cases the
predicted proton lifetime turns out to be in the border-line of experimental
limit. The predictions of the top quark mass, the mass ratio $m_b(m_b)/
m_\tau(m_\tau)$ from the two-loop evolution of Yukawa couplings and the mass of
the left handed neutrino via see-saw mechanism are summarized. The lower bounds
on the ratio of the VEVs of the two low energy doublets ($\tan\beta$) from the
requirement of the perturbative unitarity of the top quark Yukawa coupling up
to the grand unification scale are also presented. All the predictions have
been compared with those of the one-step unified theory.
