We consider hidden sector supersymmetry breakdown in the strongly coup
led heterotic Es x Es theory of Horava and Witten. Using effective fie
ld theory methods in four dimensions, we can show hat gravitational in
teractions induce soft breaking terms in the observable sector that ar
e of order of the gravitino mass. We apply these methods to the mechan
ism of gaugino condensation at the hidden wall. Although the situation
is very similar to the weakly coupled case, there is a decisive diffe
rence concerning the observable sector gaugino mass; with desirable ph
enomenological as well as cosmological consequences. (C) 1998 Elsevier
Science B.V.