  A universal model for D=4 spinning particle is constructed with the
configuration space chosen as ${\bf R}^{3,1}\times S^2$, where the sphere
corresponds to the spinning degrees of freedom. The Lagrangian includes all the
possible world--line first order invariants of the manifold. Each combination
of the four constant parameters entering the Lagrangian gives the model, which
describes the proper irreducible Poincar\'e dynamics both at the classical and
quantum levels, and thereby the construction uniformly embodies the massive,
massless and continuous helicity cases depending upon the special choice of the
parameters. For the massive case, the connection with the Souriau approach to
elementary systems is established. Constrained Hamiltonian formulation is built
and Dirac canonical quantization is performed for the model in the covariant
form. An explicit realization is given for the physical wave functions in terms
of smooth tensor fields on ${\bf R}^{3,1}\times S^2$. One-parametric family of
consistent interactions with general electromagnetic and gravitational fields
is introduced in the massive case. The spin tensor is shown to satisfy the
Frenkel-Nyborg equation with arbitrary fixed gyromagnetic ratio in a limit of
weakly varying electromagnetic field.
