  We study the effect of quenched random field disorder on a driven elastic
interface close to the depinning transition at the upper critical dimension
d_{c}=4 using the functional renormalization group. We have found that the
displacement correlation function behaves with distance x as ln(x)^{2/3} for
large x. Slightly above the depinning transition the force-velocity
characteristics is described by the equation v ~ f |ln(f)|^{2/9}, while the
correlation length behaves as L_{v} ~ f^{-1/2}|ln(f)|^{1/6}, where f=F/F_{c}-1
is the reduced driving force.
