[en] A theory of the Hanle effect in a strong electromagnetic field is developed for the case when perturbation theory is invalid. A two-level system with terms of which one possesses a zero angular momentum and the other an angular momentum of unity is considered. The probability for transition to a third level with zero angular momentum under conditions when the first two levels are in resonance with a strong field is calculated. It is shown that with increase of the field intensity the probability dependence changes from a quadratic to linear dependence. The limits of very weak and very strong fields are investigated analytically and also the case of a very strong stationary magnetic field which splits the term with a unit angular momentum. Intermediate cases are investigated with a computer. The self-similar character of the problem is emphasized. It is concluded that with increase of intensity of the electric field the resonant nature of the probability is a function of magnetic field strength disappears