If you have a poly
and need to round it out, Graphite modeling tools has GeoPoly (in polygons).
If you have a loop or a selection of verts there really isn't anything like that in max that I know of. BUT there are several awesome scripts that do it. Illusion Catalyst has Geo Edge Loop
which is just like GeoPoly but for loops.
If you don't want to go the script route. You can select the edges, and in edit poly convert to shape, which will give you a spline. You convert that to poly and run GeoPoly, then snap the verts from the original mesh to the GeoPoly piece.