  We present an action for $N=1$ supergravity in $10+2$ dimensions, containing
the gauge fields of the $OSp(1|64)$ superalgebra, i.e. one-forms $B^{(n)}$ with
$n$=1,2,5,6,9,10 antisymmetric D=12 Lorentz indices and a Majorana gravitino
$\psi$. The vielbein and spin connection correspond to $B^{(1)}$ and $B^{(2)}$
respectively. The action is not gauge invariant under the full $OSp(1|64)$
superalgebra, but only under a subalgebra ${\tilde F}$ (containing the $F$
algebra $OSp(1|32)$), whose gauge fields are $B^{(2)}$, $B^{(6)}$, $B^{(10)}$
and the Weyl projected Majorana gravitino ${1 \over 2} (1+\Gamma_{13}) \psi$.
Supersymmetry transformations are therefore generated by a Majorana-Weyl
supercharge and, being part of a gauge superalgebra, close off-shell. The
action is simply $\int STr ({\bf R}^6 {\bf \Gamma})$ where ${\bf R}$ is the
$OSp(1|64)$ curvature supermatrix two-form, and ${\bf \Gamma}$ is a constant
supermatrix involving $\Gamma_{13}$ and breaking $OSp(1|64)$ to its ${\tilde
F}$ subalgebra. The action includes the usual Einstein-Hilbert term.
