A theory is developed for the magneto-optic Kerr effect (MOKE) excited via an optical near field. The model under consideration includes a semi-infinite ferromagnet and a small non- magnetic metal particle which is located nearby and possesses a long-living surface plasmon. A multiple-scattering formulation of the problem is given. Considering the Rayleigh scattering of light and the magneto-optical light polarization conversion as elementary events, all the essential optical processes are classified, and those which contribute to the near-field MOKE are treated separately. An effective particle polarizability, responsible for a near-field excitation, is treated self-consistently to all orders in light-matter scattered light field is discussed with special emphasis on the change of optical polarization due to MOKE.