  The AdS/CFT correspondence of elementary string theory has been recently
suggested as a ``microscopic'' approach to QCD string theory in various
dimensions. We use the microscopic theory to show that the ultraviolet regime
on the string world-sheet is mapped to the ultraviolet effects in QCD. In the
case of QCD_2, a world-sheet path integral representation of QCD strings is
known, in terms of a topological rigid string theory whose world-sheet
supersymmetry is reminiscent of Parisi-Sourlas supersymmetry. We conjecture
that the supersymmetric rigid string theory is dual to the elementary Type IIB
string theory in the singular AdS background that corresponds to the large-N
limit of QCD_2. We also generalize the rigid string with world-sheet
Parisi-Sourlas supersymmetry to dimensions greater than two, and argue that the
theory is asymptotically free, a non-zero string tension is generated
dynamically through dimensional transmutation, and the theory is topological
only asymptotically in the ultraviolet.
