We explore the one-loop electroweak radiative corrections in the minimal
SU(5) and the no-scale flipped SU(5) supergravity models via explicit
calculation of vacuum polarization contributions to the ϵ1,2,3​
parameters. Experimentally, ϵ1,2,3​ are obtained from a global fit
to the LEP observables, and MW​/MZ​ measurements. We include q2-dependent
effects which have been neglected in most previous ``model-independent"
analyses of this type. These effects induce a large systematic negative shift
on ϵ1,2,3​ for light chargino masses (m_{\chi^\pm_1}\lsim70\GeV).
In agreement with previous general arguments, we find that for increasingly
large sparticle masses, the heavy sector of both models rapidly decouples, \ie,
the values for ϵ1,2,3​ quickly asymptote to the Standard Model
values with a {\it light} Higgs (m_{H_{SM}}\sim100\GeV). Specifically, at
present the 90% CL upper limit on the top-quark mass is m_t\lsim175\GeV in
the no-scale flipped SU(5) supergravity model. These bounds can be
strengthened for increasing chargino masses in the 50-100\GeV interval. In
particular, for m_t\gsim160\GeV, the Tevatron may be able to probe through
gluino(g~​) and squark(q~​) production up to m_{\tilde g}\approx
m_{\tilde q}\approx250\GeV, exploring at least half of the parameter space in
this model.Comment: 15 pages,(6 ps figures available upon request), TeX(harvmac),
CTP-TAMU-19/93, ACT-07/9