This paper reports on the results of ab initio calculations of the electronic and magnetic properties of Si digital heterostructures doped with a Fe monolayer of the substintutional or interstitial type. It has been revealed that, after the structural relaxation, heterostructures of both types exhibit a two-dimentional metallic behavior and a ferromagnetic ordering in the range of Si spacer thicknesses up to 19 atomic layers. The magnetization and spin polarization at the Fermi level for the heterostuctures woth an Fe monolayer of the substitional type are two times higher than those for the system with an Fe monolyer of the interstitial type.