Numerous radar observations demonstrate anomalously strong electron heating in polar electrojets during magnetic storms. The effect often correlates with the onset of the Farley-Buneman instability caused by strong convection electric field. Anomalous heating of electrons is usually attributed to turbulent electric fields developing in the E region due to that instability. We propose a theoretical model of the effect based on heuristic assumptions on nonlinearly saturated turbulence and equations of the electron and ion energy budget. The model has been quantitatively tested in the companion paper by Milikh and Dimant <2003>. Good agreement with observations supports the implied physical mechanism.