We show that the Hamiltonian systems on Sternberg-Wein-
stein phase spaces which yield Wong’s equations of motion for
a classical particle in a gravitational and a Yang-Mills field,
naturally arise as the first order approximation of generic
Hamiltonian systems on Poisson manifolds at a critical La-
grangian submanifold. We further define a second order ap-
proximated system involving scalar fields which first appeared
in Einstein-Mayer theory. Reduction and symplectic realiza-
tion of this system are interpreted in terms of dimensional
reduction and Kaluza-Klein theory.