  The $|\Delta S|=1$ $\Lambda N$ interaction, responsible for the decay of
hypernuclei, is studied by means of an Effective Field Theory where the long
range physics is described by pion and kaon exchange mechanisms, and its short
range counterpart is obtained from the most general non-derivative local
four-fermion interaction. We show that, including the Lowest Order Parity
Conserving contact terms, allows us to reproduce the total decay rates for
$^5_\Lambda {\rm He}$, $^{11}_\Lambda {\rm B}$ and $^{12}_\Lambda {\rm C}$ with
a reasonable value of ${\hat \chi^2}$, while in order to get a prediction for
the Parity Violating (PV) asymmetry compatible with experiments, we have to
include the Lowest Order PV contact pieces.
