  The dephasing effect of metallic gates on electrons moving in one
quasi--one--dimensional diffusive wires is analyzed. The incomplete screening
in this geometry implies that the effect of the gate can be described, at high
energies or temperatures, as an electric field fluctuating in time. The
resulting system can be considered a realization of the Caldeira-Leggett model
of an environment coupled to many particles. Within the range of temperatures
where this approximation is valid, a simple estimation of the inverse dephasing
time gives $\tau_{\rm G}^{-1} \propto T^{1/2}$.
