Analytical approaches are developed to describe the thermal disordering of surfaces in noble-gas crystals, based on the Lennard-Jones interaction potential. The roughness of faces with different orientations is described by means of a quasi-lattice model, where the repulsive forces and the contributions of vibrational degrees of freedom are taken into account in the free surface energy. It is shown, that the free surface energy becomes isotropic near the melting temperature. The surface melting is described by the weighted-density functional method. The face-orientation dependences of surface melting and the melt structurization near crystal surface are studied. The effect of long-range Coulomb forces on the atomic structure of the crystal-melt interface is considered. (author). 15 refs, 5 figs.