  Locally homogeneous CR-manifolds in dimension 3 were classified, up to local
CR-equivalence, by E.Cartan. We classify, up to local CR-equivalence, all
locally homogeneous CR-manifolds in dimension 4. The classification theorem
enables us also to classify all symmetric CR-manifolds in dimension 4, up to
local biholomorphic equivalence. We also prove that any 4-dimensional real Lie
algebra can be realized as an algebra of affine vector fields in a domain in
$\CC{3}$, linearly independent at each point.
