  In this short note we prove an equivariant version of the formality of
multidiffirential operators for a proper Lie group action. More precisely, we
show that the equivariant Hochschild-Kostant-Rosenberg quasi-isomorphism
between the cohomology of the equivariant multidifferential operators and the
complex of equivariant multivector fields extends to an
$L_\infty$-quasi-isomorphism. We construct this $L_\infty$-quasi-isomorphism
using the $G$-invariant formality constructed by Dolgushev. This result has
immediate consequences in deformation quantization, since it allows to obtain a
quantum moment map from a classical momentum map with respect to a
$G$-invariant Poisson structure.
