In this paper, a novel algorithm for computing Physical Optics (PO) integrals is introduced. In this method, the integration problem is converted to an inverse problem by Levin's integration algorithm. Furthermore, the singularities, that are possible to occur in the applications of Levin's method, are handled by employing trapezoidal rule together with Levin's method. Finally, the computational accuracy of this new method is checked for some radar cross section (RCS) estimation problems performed on flat, singlycurved and doubly-curved PEC plates which are modeled by 8-noded isoparametric quadrilaterals. The results are compared with those obtained by analytical and brute force integration.