Magnetic storms are distinguishable from other periods of geomagnetic activity by the injection of trapped electrons and ions to the 2≲L≲4 region. It has been proposed previously that this injection results from an inward displacement of the preexisting trapped-particle population by enhanced storm time electric fields. However, high-energy (>40 keV) ring-current particles have drift periods that are typically shorter than the time of the main-phase development, and so the direct radial transport of these particles is restricted. We propose here that the transport of >40 keV particles into the storm time ring current can result from enhanced stochastic radial transport driven by fluctuating electric fields during a storm's main phase. We estimate the effects of such electric fields by applying radial-diffusion theory, assuming a preexisting trapped-particle population as the initial condition, and we demonstrate the feasibility of explaining observed flux increases of >40-keV particles at L≲4 by enhanced radial ''diffusion.'' It is necessary that new particles be injected near the outer boundary of the trapping region so as to maintain the fluxes there as an outer boundary condition, and we estimate that the >40-keV portion of the storm time ring current at L~3 consists of about 50% preexisting and about 50% new particles. We find that the required root-mean-square intensity of the field fluctuations is ~1--1.5 mV/m during the main phase, as compared with a long-term average value ~0.25 mV/m. Available ground-based radar observations suggest that the required storm time intensities are in fact present. We thus find that formation of the storm time ring current may be explainable via a combination of direct radial transport at energies ≲40 keV and ''diffusive'' radial transport at higher energies. ¿ American Geophysical Union 1989