  An SU(3)_L x U(1)_N gauge model, where E^{-i} (i=1,2,3) as heavy leptons are
placed in the third member of lepton triplets, is shown to provide the large
mixing angle (LMA) MSW solution to the solar neutrino problem. By introducing
approximate conservation of L_e-L_mu-L_tau (\equiv L') into the model, we have
estimated \Delta m_\odot^2 \sim \sqrt{2}\epsilon \Delta
m_{atm}^2m_{E^1}/(m_{E^2}+m_{E^3}), where \epsilon represents L'-breaking
effects and m_{E^i} is a mass of E^{-i}. Since \Delta m_{atm}^2 \sim 3 x
10^{-3} eV^2, the LMA solution is obtained for \epsilon\sim 0.01-0.1 in the
case of m_{E^1} \sim m_{E^{2,3}}. This mechanism utilizes two-loop radiative
mechanism, which contains a triplet version of the singly charged Zee boson,
h^+, given by \xi = (\xi^{++}, {\bar \xi}^+, h^+)^T. Almost bimaximal mixing is
dynamically realized by the approximate equality between the \xi-couplings of
the first family to the second and third families.
