  We show that the currently experimentally preferred values of the top-quark
mass (\ie, $130\lsim m_t\lsim180\GeV$) are naturally understood in the context
of string models, where the top-quark Yukawa coupling at the string scale is
generically given by $\lambda_t={\cal O}(g)$, with $g$ the unified gauge
coupling. A detailed study of the Yukawa sector of $SU(5)\times U(1)$
supergravity shows that the ratio of the bottom-quark to tau-lepton Yukawa
couplings at the string scale is required to be in the range
$0.7\lsim\lambda_b/\lambda_\tau\lsim1$, depending on the values of $m_t$ and
$m_b$. This result is consistent with $SU(5)\times U(1)$ symmetry, which does
{\em not} require the equality of these Yukawa couplings in the unbroken
symmetry phase of the theory. As a means of possibly predicting the value of
$m_t$, we propose a procedure whereby the size of the allowed parameter space
is determined as a function of $m_t$, since all sparticle and Higgs-boson
masses and couplings depend non-trivially on $m_t$. At present, no significant
preference for particular values of $m_t$ in $SU(5)\times U(1)$ supergravity is
observed, except that high-precision LEP data requires $m_t\lsim180\GeV$.
