neutrinos via a hierarchical mass spectrum. We specifically focus on the LMA MSW solution in the text, with the LOW and SMA MSW solutions relegated to Appendices.

The layout of the remainder of the paper is as follows. In section II we briefly review the see-saw mechanism in the Minimal Supersymmetric Standard Model (MSSM) [@MSSM] with right-handed neutrinos. In section III we review some useful analytic results for SRHND, for the case of an approximately diagonal right-handed Majorana mass matrix. In section IV we introduce the string-inspired Pati-Salam model, and in section V we introduce an Abelian anomalous gauge $U(1)_X$ family symmetry into the model, and show how horizontal Yukawa hierarchies may be generated. In section VI we describe our operator approach to fermion masses, including the heavy Majorana neutrino masses. Section VII contains the main results of the paper. In this section we show how a particular choice of $U(1)_X$ family charges, and operators with certain Clebsch coefficients can lead to a successful description of quark and lepton masses and mixing angles, and in particular describe atmospheric and solar neutrinos via SRHND. Although the neutrino masses and mixing angles correspond to the usual LMA MSW solution, in Appendix C 