  Using a level-raising argument (and a result of Larsen on the image of Galois
representations in compatible systems), we prove that for any automorphic
representation $\pi$ for $\U(3)$, the $l$-adic Galois representation $\rho_l$
which is attached to $\pi$ by the work of Blasius and Rogawski, is the one
expected by local Langlands correspondance at every finite place (at least up
to semi-simplification and for a density one set of primes $l$). We rely on the
work of Harris and Taylor, who have proved the same results (for $\U(n)$)
assuming the base change of $\pi$ is square-integrable at one place. As a
corollary, every automorphic representation which is tempered at an infinite
number of places is tempered at every places.
