We show that supersymmetry can be broken mainly by hidden matter condensates in the observable matter direction in generic superstring models. This happens only when the fields whose VEV`s give masses to hidden matter do not decouple at the condensation scale. We find how the parameters of the string model and the vacuum determine whether supersymmetry is broken mainly by hidden matter or gaugino condensates and in the matter or moduli direction. (author). 12 refs.