A previous study (Prakash, 1989) to model the nonlinear interaction between the kinetic Alfven wave and a bouncing proton trapped in the magnetosphere included only the longitudinal electric field component of the kinetic Alfven wave in the analysis. Despite the simplicity of the field configuration used in that model, its results provided a possible explanation for energetic proton precipitation to the polar region by alluding to the breakdown of the second adiabatic invariant of motion as a result of the onset of chaos in the particle motion. Since the corresponding transverse component of the wave electric field is an order of magnitude larger and since the longitudinal and transverse motions of the proton are coupled, this transverse electric field component is included along with the longitudinal component in the formulation of the present work. It increases the number of coupled equations of the Hamiltonian system from two to four. By using the Lyapunov exponent analysis, the chaotic nature of this five-dimensional system is examined. It is shown that the threshold field is lowered by at least a factor of 6 and thus is much more easily exceeded under the normal magnetospheric condition. Furthermore, the results also show that protons drift radially when chaos occurs. It may explain the observation of low-altitude trapped energetic protons in the equatorial region (Guzik et al., 1989). ¿ American Geophysical Union 1994