Virasoro orbits, AdS(3) quantum gravity and entropy

We analyse the canonical structure of AdS(3) gravity in terms of the coadjo int orbits of the Virasoro group. There is one subset of orbits, associated to BTZ black hole solutions, that can be described by a pair of chiral fre e fields with a background charge. There is also a second subset of orbits, associated to point-particle solutions, that are described by two pairs of chiral free fields obeying a constraint. All these orbits admit Kahler qua ntization and generate a Hilbert space which, despite of having Delta(0)(<( Delta)over bar>(0)) = 0, does not provide the right degeneracy to account f or the Bekenstein-Hawking entropy due to the breakdown of modular invarianc e. Therefore, additional degrees of freedom, reestablishing modular invaria nce, are necessarily required to properly account for the black hole entrop y.