Satellite observations have revealed that the flux variations of outer belt relativistic electrons during the main phase of a magnetic storm exhibit a strong radial dependence. This L dependence is characterized as a small increase or decrease near the inner edge of the belt (L ~ 3) and a large decrease inits outer region (L ~ 5). Extending the study by Kim and Chan <1997> of relativistic electron flux decreases at geostationary orbit, we investigate the characteristic radial dependence in terms of the fully adiabatic response of relativistic electrons to magnetic field perturbations. Using Liouville's theorem and the conservation of the first and third adiabatic invariants, we calculate storm main phase fluxes of equatorially mirroring electrons by adiabatically evolving the prestorm values. A quiet time electron distribution model is constructed from the CRRES satellite data. The radial structure of magnetic field perturbations and the spatial and energy dependence of the quiet time electron distribution are found to affect the main phase fluxes through adiabatic processes. In response to the field perturbations, adiabatic flux changes become larger at higher L shells where electrons can experience strong deceleration and considerable radial displacement. The nonmonotonic energy spectrum at the inner edge of the outer belt, which is featured in our quiet time electron model, can yield a slight flux increase in that region even during adiabatic deceleration. The results of this study suggest that a fully adiabatic treatment can provide an important component of the explanation for the general pattern of large scale changes in the radial profile of relativistic electron fluxes during the storm main phase.