This paper reports the study by electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) of lithium particles in Li2O powders irradiated by 1-MeV electrons. The metallic lithium particles are characterized by a narrow ESR line (Delta B-pp = 0.013 mT) due to conduction electrons and an ENDOR signal from Li-7 nuclei interacting with these electrons. The ESR of conduction electrons in lithium particles exhibits a bistable hysteresis of 0.18 mT width at T = 4 K due to steady-state bistable dynamic nuclear polarization by the Overhauser effect, in good agreement with theoretical predictions. The analysis of the bistable conduction electron spin resonance (BCESR) line shape showed the existence of two populations of particles differing by their electron spin relaxation times T-2 and characterized by a distribution of nuclear relaxation times.