  We discuss rare meson decays $K^ + \to \pi ^ - \ell ^ + \ell '^ +$ and $D^ +
\to K^ - \ell ^ + \ell '^ +$ ($\ell ,\ell ' = e,\mu $) in a supersymmetric
extension of the standard model with explicit breaking of R-parity by bilinear
Yukawa couplings in the superpotential. Estimates of the branching ratios for
these decays are given. We also compare our numerical results with analogous
ones previously obtained for two other mechanisms of lepton number violation:
exchange by massive Majorana neutrinos and trilinear R-parity violation.
