  An extension of the Standard Model to the local gauge group $SU(3)_c\otimes
SU(3)_L\otimes U(1)_X$ which is a subgroup of the electroweak-strong
unification group $E_6$ is analyzed. The mass scales, the gauge boson masses,
and the masses for the spin 1/2 particles in the model are calculated. The mass
differences between the up and down quark sectors, between the quarks and
leptons, and between the charged and neutral leptons in one family are
explained as a consequence of mixing of ordinary with exotic fermions implied
by the model. By using experimental results we constrain the mixing angle
between the two neutral currents and the mass of the additional neutral gauge
boson to be $-0.0015 \leq \sin\theta \leq 0.0048$ and $600 GeV \leq M_{Z_2}$ at
95% CL. The existence of a Dirac neutrino for each family with a mass of the
order of the electroweak mass scale is predicted.
