[en] General formulation of the steady state obtained by an r.f. confinement of plasma is presented within the framework of the collisionless two-fluid model. The effect of plasma flow is taken into account by introducing modified scalar and vector potentials, modification being due to the centrifugal force and the Coriolis force, respectively. A simple variation principle is derived to determine the steady state using the Clebsch representation for the modified vector potential. For the axisymmetric case, expressions or equations for quasilinear modification of the average quantities are derived in the weak-field approximation. Results of numerical calculation for the r.f. plugging applied to a line cusp are presented and discussed. (author)