  We develop a relativistic covariant and unitary description of the
pion-nucleon interaction in a hadron-exchange model. The model is based on the
solution of a dimensionally reduced (quasipotential) Bethe-Salpeter equation
for the partial-wave off-shell $\pi N$ scattering amplitudes with the potential
consisting of the field-theoretical $s$- and $u$-channel nucleon, Roper, Delta,
$D_{13}$, $S_{11}$ exchanges, and the $t$-channel $\rho$ and $\sigma$ meson
exchanges. The contributions of the spin-3/2 Delta and $D_{13}$ resonances are
treated within the Rarita-Schwinger formalism and different forms of the $\pi
N\Delta$ vertex are investigated. The free parameters of the model are fitted
to the $\pi N$ phase-shift data of the KH80 and SM95 partial-wave analyses in
the region up to 600 MeV pion kinetic energy. The resulting on-shell solution
provides a good description of the $\pi N$ scattering lengths, as well as the
energy behavior of the S, P, and D partial waves. The sensitivity of the phase
shifts on various model-dependent effects is examined.
