  The low-energy D=4, N=1 effective action of the strongly coupled heterotic
string is explicitly computed by compactifying Horava-Witten theory on the
deformed Calabi-Yau three-fold solution due to Witten. It is shown that, to
order kappa^{2/3}, the Kahler potential is identical to that of the weakly
coupled theory. Furthermore, the gauge kinetic functions are directly computed
to order kappa^{4/3} and shown to receive a non-vanishing correction. Also, we
compute gauge matter terms in the Kahler potential to the order kappa^{4/3} and
find a nontrivial correction to the dilaton term. Part of those corrections
arise from background fields that depend on the orbifold coordinate and are
excited by four-dimensional gauge field source terms.
