  We consider the formulation and quantization of the N=3 superparticle model,
both with and without central charge. Without the central charge the action
possesses U(3) invariance and therefore is naturally quantized in the N=3
harmonic superspace. The quantization reproduces the N=3 supergauge strength
multiplets, described by analytic N=3 superfields and a gravitino multiplet as
a constrained N=3 chiral superfield. When the central charge is present, it
breaks the U(3) R-symmetry of N=3 superalgebra down to SU(2)xU(1), and the
corresponding superparticle model is formulated in the N=2 harmonic superspace
extended by a pair of extra Grassmann variables. The quantization of such a
model leads to the massive BPS N=3 vector multiplet. It is shown that upon
additional superfield constraints such multiplet reduces to the massive N=2
vector multiplet.
