  We study the competition between long- and short-range interactions among
charge carriers in strongly-correlated electronic systems employing a new
method which combines the density-matrix renormalization-group technique with a
self-consistent treatment of the long-range interactions.
  We apply the method to an extended t-J model which exhibits ``stripe'' order.
The Coulomb interactions, while not destroying stripes, induce large transverse
stripe fluctuations with associated charge delocalization. This leads to a
substantial Coulomb-repulsion-induced {\it enhancement} of long-range
superconducting pair-field correlations.
