  In this paper, we determine the group of contact transformations modulo
contact isotopies for Legendrian circle bundles over closed surfaces of
nonpositive Euler characteristic. These results extend and correct those
presented by the first author in a former work. The main ingredient we use is
connectedness of certain spaces of embeddings of surfaces into contact
3-manifolds. In the third section, this connectedness question is studied in
more details with a number of (hopefully instructive) examples.
