A MODEL FOR F-L AND R=F-L F-T AT LOW-X AND LOW-Q(2)/

A model for the longitudinal structure function F-L at low x and low Q (2) is presented, which includes the kinematical constraint F-L simila r to Q(4) as Q(2) --> 0. It is based on the photon-gluon fusion mechan ism suitably extrapolated to the region of low Q(2). The contribution of quarks having limited transverse momentum is treated phenomenologic ally assuming that it is described by the soft pomeron exchange mechan ism. The ratio R = F-L/(F-2 - F-L), with the F-2 appropriately extrapo lated to the region of low Q(2), is also discussed.