Abstract: In order to facilitate a shape-keeping compression in a process of fabricating an elongated glass-body, particularly a preform for optical waveguides on the basis of SiO.sub.2 in which, from a powdery glass starting material a porous body is formed and sintered into a glass body, there is provided a process in which the filling of the powdery glass starting material into the compression mold is carried out by simultaneously effecting a precompaction and in which, following the fill-in operation, the pre-compacted powdery material is compressed to obtain the porous body. Steps and measures are proposed for stabilizing the flexible hose which is preferably used as a compression mold, in its shape during the fill-in process. For the filling-in of the material there is used a screw conveyor or an arrangement of several screw conveyors arranged coaxially or next to each other, in order to form a porous body having the desired radial material composition.