[GRASS-user] Multiple 3D DGN files Import with Z-value flag

Is there a way, how to import multiple 3D GDN files into a GRASS mapset? My DGN files include only Polylines of terrain contours from which I need to build a DEM. I use GRASS 6.4.2 for MS-Windows (WinXP, latest stable version).
Thank You for any idea.
Martin Kresac