The motion of the Jupiter-Saturn planetary system near the 5 : 2 mean-motion resonance is modeled analytically in the frame of the planar general three-body problem. The topology of the phase space in the resonance and near-resonance domains is investigated in detail by means of surfaces of section and spectral map techniques. Various regimes of motion of the Jupiter-Saturn system are observed, and their domains are represented on the parameter plane defined by the total energy of the system and the parameter of proximity to the 5 : 2 resonance. The regions of transition between domains of different regimes of motion are characterized by chaotic motion. We show that there is a significant chaotic zone associated with the 5 : 2 mean-motion resonance, but large-scale excursions of the planet eccentricities are not possible in the planar three-body model.