The authors have formulated a theory of interaction between waves having frequencies much lower than the cyclotron frequency and trapped particles in tokamaks. They have obtained a criterion for stochastic transition due to the overlapping of the wave-particle bounce resonances. Collisional stochasticity is studied in a case where this criterion is not satisfied. It is shown that, depending on the relationship between the time of the collisional transition to stochasticity, the bounce period of particle motion in a toroidal field and the oscillation period for particle energy in the superposition of the tokamak magnetic field and the wave field, there may be three different regimes (of weak, moderate and strong oscillations). Equations describing the effect of the RF field on the distribution function of trapped particles have been derived. By means of these equations, some consequences concerning the RF power absorption by trapped particles have been identified.