  We calculate the gravitational self force acting on a pointlike particle of
mass $\mu$, set in a circular geodesic orbit around a Schwarzschild black hole.
Our calculation is done in the Lorenz gauge: For given orbital radius, we first
solve directly for the Lorenz-gauge metric perturbation using numerical
evolution in the time domain; We then compute the (finite) back-reaction force
from each of the multipole modes of the perturbation; Finally, we apply the
``mode sum'' method to obtain the total, physical self force. The {\em
temporal} component of the self force (which is gauge invariant) describes the
dissipation of orbital energy through gravitational radiation. Our results for
this component are consistent, to within the computational accuracy, with the
total flux of gravitational-wave energy radiated to infinity and through the
event horizon. The {\em radial} component of the self force (which is gauge
dependent) is calculated here for the first time. It describes a conservative
shift in the orbital parameters away from their geodesic values. We thus obtain
the $O(\mu)$ correction to the specific energy and angular momentum parameters
(in the Lorenz gauge), as well as the $O(\mu)$ shift in the orbital frequency
(which is gauge invariant).
