  A simple extension of the Standard Model (SM), based on the gauge group
$SU(3)_C\otimes SU(3)_L\otimes U(1)_Y$ with $Y$ being the hypercharge, is
considered. We show that, by imposing an approximate global $SU(2)_L\times
SU(2)_R$ custodial symmetry at the SM energy scale, the $Z-Z'$ mixing is absent
at tree level and the value of the $\rho$ parameter can be kept close to one.
Tree-level flavor-changing neutral currents are also reduced to three
particles, namely $Z'$, a CP-odd Higgs and a CP-even Higgs. The model predicts
new leptons with electric charges of $\pm 1/2e$ and new quarks with $\pm 1/6e$
charges as well as new gauge and scalar bosons with $\pm 1/2e$ charges.
Electric charge conservation requires that one of them must be stable. Their
masses are unfortunately free parameters.
