  (abriged) MRI turbulence is a leading mechanism for the generation of an
efficient turbulent transport of angular momentum in an accretion disk through
a turbulent viscosity effect. It is believed that the same process could also
transport large-scale magnetic fields in disks, reshaping the magnetic
structures in these objects. This process, known as turbulent resistivity, has
been suggested and used in several accretion-ejection models and simulations to
produce jets. Still, the efficiency of MRI-driven turbulence to transport
large-scale magnetic fields is largely unknown.
  We investigate this problem both analytically and numerically. We introduce a
linear calculation of the MRI in the presence of a spatially inhomogeneous mean
magnetic field. We show that, in this configuration, MRI modes lead to an
efficient magnetic field transport, on the order of the angular momentum
transport. We next use fully non linear simulations of MRI turbulence to
compute the turbulent resistivity in several magnetic configurations.
  We find that the turbulent resistivity is on the order of the turbulent
viscosity in all our simulations, although somewhat lower. The turbulent
resistivity tensor is found to be highly anisotropic with a diffusion
coefficient 3 times greater in the radial direction than in the vertical
direction.
  These results support the possibility of driving jets from turbulent disks;
the resulting jets may not be steady.
