  We implement an effective operator formalism for general one- and two-body
operators, obtaining results consistent with the no-core shell model (NCSM)
wave functions. The Argonne V8' nucleon-nucleon potential was used in order to
obtain realistic wave functions for 4He, 6Li and 12C. In the NCSM formalism, we
compute electromagnetic properties using the two-body cluster approximation for
the effective operators and obtain results which are sensitive to the range of
the bare operator. To illuminate the dependence on the range, we employ a
Gaussian two-body operator of variable range, finding weak renormalization of
long range operators (e.g., quadrupole) in a fixed model space. This is
understood in terms of the two-body cluster approximation which accounts mainly
for short-range correlations. Consequently, short range operators, such as the
relative kinetic energy, will be well renormalized in the two-body cluster
approximation.
