  We revisit quantum gravitational contributions to quantum gauge field
theories in the gauge condition independent Vilkovisky-DeWitt formalism based
on the background field method. With the advantage of Landau-DeWitt gauge, we
explicitly obtain the gauge condition independent result for the quadratically
divergent gravitational corrections to gauge couplings. By employing, in a
general way, a scheme-independent regularization method that can preserve both
gauge invariance and original divergent behavior of integrals, we show that the
resulting gauge coupling is power-law running and asymptotically free. The
regularization scheme dependence is clarified by comparing with results
obtained by other methods. The loop regularization scheme is found to be
applicable for a consistent calculation.
