We provide a detailed study of the phenomenology of orbifold
compactifications of the heterotic string within the context of supergravity
effective theories. Our investigation focuses on those models where the soft
Lagrangian is dominated by loop contributions to the various soft supersymmetry
breaking parameters. Such models typically predict non-universal soft masses
and are thus significantly different from minimal supergravity and other
universal models. We consider the pattern of masses that are governed by these
soft terms and investigate the implications of certain indirect constraints on
supersymmetric models, such as flavor-changing neutral currents, the anomalous
magnetic moment of the muon and the density of thermal relic neutralinos. These
string-motivated models show novel behavior that interpolates between the
phenomenology of unified supergravity models and models dominated by the
superconformal anomaly.Comment: 47 pages, 14 figure