  A variational technique to describe the ground and scattering states below
the break-up threshold for a three-nucleon system is developed. The method
consists in expanding the wave function in terms of correlated Harmonic
Hyperspherical functions suitable to handle the large repulsion contained in
the nuclear potential at short distances; three body forces have also been
considered. The inclusion of the pp Coulomb repulsion in the p-d processes does
not cause any particular problem, since no partial wave decomposition of the
interaction is performed. Accurate numerical results are given for ground state
properties and scattering lenghts, phase shifts and mixing parameters at three
different energies of the incident nucleon. The agreement with other available
results and with experimental analyses is higlly satisfactory.
