  We have performed a search for the decays $B^+\to J/\psi p \bar{\Lambda}$ and
$B^0\to J/psi p \bar{p}$ in a data set of $(88.9 \pm 1.0)\times 10^6$
$\Upsilon(4S)$ decays collected by the BaBar experiment at the PEP-II $\e^+e^-$
storage ring at the Stanford Linear Accelerator Center. Four charged $B$
candidates have been observed with an expected background of $0.21\pm 0.14$
events. The corresponding branching fraction is $12^{+9}_{-6}\times 10^{-6}$,
where statistical and systematic uncertainties have been combined. The result
can be interpreted as a 90% confidence level (CL) upper limit of $26 \times
10^{-6}$. We also find one $B^0$ candidate, with an expected background of
$0.64\pm 0.17$ events, implying a 90% CL upper limit of $1.9 \times 10^{-6}$.
