A magnetic field integral equation method for the solution of propagation problems over large smoothly undulating surfaces is discussed. Unlike conventional methods that assume invariance of surface height transverse to the direction of propagation, we incorporate the effects of moderate transverse gradients along a radial profile. In this formulation, vertical and horizontal polarizations are coupled, and a vector integral equation must be solved along a radial path, in a quasi-three-dimensional approach. This provides a first-order correction modeling the depolarizing effects of transverse gradients. Off radial diffraction and multipath effects are neglected in the scheme. Numerical comparison is made with existing two-dimensional integral equation solutions, the uniform theory of diffraction, and measured data.