[en] The structure of a surface barrier, in the frame of the general critical-state theory, of a type II superconducting slab subjected to parallel magnetic fields (in which the direction of the dc bias and ac field are left arbitrary) has been incorporated in this paper. The internal magnetic field distribution has been developed. In the case of the amplitude of ac field (b_O) less than the magnitude of the dc bias field (B_O), analytic expressions for ac losses are obtained. Maximum values of FL cutting and flux-pinning losses are also determined. A good agreement with the previous results (in this case of α_O=O with absence of surface barrier effects) is obtained. (author)