  We consider a class of well motivated string-inspired flipped $SU(5)$
supergravity models which include four supersymmetry breaking scenarios:
no-scale, strict no-scale, dilaton, and special dilaton, such that only three
parameters are needed to describe all new phenomena $(m_t,\tan\beta,m_{\tilde
g})$. We show that the LEP precise measurements of the electroweak parameters
in the form of the $\epsilon_1$ variable, and the CLEOII allowed range for
$\bsg$ are at present the most important experimental constraints on this class
of models. For $m_t\gsim155\,(165)\GeV$, the $\epsilon_1$ constraint (at
90(95)\%CL) requires the presence of light charginos
($m_{\chi^\pm_1}\lsim50-100\GeV$ depending on $m_t$). Since all sparticle
masses are proportional to $m_{\tilde g}$, $m_{\chi^\pm_1}\lsim100\GeV$
implies: $m_{\chi^0_1}\lsim55\GeV$, $m_{\chi^0_2}\lsim100\GeV$, $m_{\tilde
g}\lsim360\GeV$, $m_{\tilde q}\lsim350\,(365)\GeV$, $m_{\tilde
e_R}\lsim80\,(125)\GeV$, $m_{\tilde e_L}\lsim120\,(155)\GeV$, and
$m_{\tilde\nu}\lsim100\,(140)\GeV$ in the no-scale (dilaton) flipped $SU(5)$
supergravity model. The $\bsg$ constraint excludes a significant fraction of
the otherwise allowed region in the $(m_{\chi^\pm_1},\tan\beta)$ plane
(irrespective of the magnitude of the chargino mass), while future experimental
improvements will result in decisive tests of these models. In light of the
$\epsilon_1$ constraint, we conclude that the outlook for chargino and
selectron detection at LEPII and at HERA is quite favorable in this class of
models.
