  A two-leg ladder with $n$-component fermionic fields in the chains has been
considered using an analytic renormalization group method. The fixed points and
possible phases have been determined for generic filling as well as for a
half-filled system and for the case when one of the subbands is half filled. A
weak-coupling Luttinger-liquid phase and several strong-coupling gapped phases
have been found. In the Luttinger liquid phase, for the most general spin
dependence of the couplings, all $2n$ modes have different velocities if the
interband scattering processes are scaled out, while $n$ doubly degenerate
modes appear if the interband scattering processes remain finite. The role of
backward-scattering, charge-transfer and umklapp processes has been analysed
using their bosonic form and the possible phases are characterized by the
number of gapless modes. As a special case the SU($n$) symmetric Hubbard ladder
has been investigated numerically. It was found that this model does not scale
to the Luttinger liquid fixed point. Even for generic filling gaps open up in
the spectrum of the spin or charge modes, and the system is always insulator in
the presence of umklapp processes.
