  The contributions of scalar and gauge leptoquarks into widths of $K^0_L \to
e^{\mp} \mu^{\pm}$, $B^0 \to e^{\mp} \tau^{\pm}$ decays are calculated in the
models with the vectorlike and chiral four color symmetry and with the Higgs
mechanism of the quark-lepton mass splitting. From the current data on $K^0_L$
and $B^0$ decays the mass limits for scalar and chiral leptoquarks and the
updated vector leptoquark mass limits are obtained. It is shown that unlike the
gauge leptoquarks the scalar leptoquark mass limits are weak, of order or below
their direct mass limits. The search for such scalar leptoquarks at LHC and the
further search for leptonic decays $ B^0 \to l^+_i l^-_j $ are of interest.
