  We present a weak gravitational lensing analysis of 22 early-type strong lens
galaxies, based on deep HST images obtained as part of the Sloan Lens ACS
Survey. Using the most advanced techniques to control systematic uncertainties
related to the variable PSF and charge transfer efficiency of the ACS, we
detect weak lensing signal out to 300 kpc/h. We analyze blank control fields
from the COSMOS survey in the same manner, inferring that the residual
systematic uncertainty in the tangential shear is <0.3%. A joint strong and
weak lensing analysis shows that the average total mass density profile is
consistent with isothermal over two decades in radius (3-300 kpc/h,
approximately 1-100 Reff). This finding extends by over an order of magnitude
in radius previous results, based on strong lensing and/or stellar dynamics,
that luminous and dark component ``conspire'' to form an isothermal mass
distribution. In order to disentangle the contributions of luminous and dark
matter, we fit a two-component mass model (R^1/4 + NFW) to the weak and strong
lensing constraints. It provides a good fit to the data with only two free
parameters; i) the average stellar mass-to-light ratio M_*/L_V=4.48 +- 0.46
hMo/Lo, in agreement with that expected for an old stellar population; ii) the
average virial mass-to-light ratio M_vir/L_V = 246+101-87 hMo/Lo. [abridged]
