The nonlinear interaction of powerful radio waves with nonresonant density fluctuations in a nonuniform weakly ionized magnetoplasma is considered. It is shown that the interaction can generate a high-frequency radio wave envelope, which generally is governed by a nonlinear Schr¿dinger equation. Accounting for the dependence of the attachment frequency on the radiation intensity, as well as the differential Joule heating nonlinearity, we derive the equations for the nonthermal electron density and temperature perturbations. The various nonlinear terms in the electron motion are compared. The implications of our investigation for the filamentation of radio waves in the lower part of the Earth's ionosphere are pointed out. ¿ American Geophysical Union 1992