  The off mass shell continuation of dual amplitude with Mandelstam analyticity
(DAMA) is proposed. The modified DAMA (M-DAMA) preserves all the attractive
properties of DAMA, such as its pole structure and Regge asymptotics, and leads
to a generalized dual amplitude A(s,t,Q^2). In such a way we complete a unified
"two-dimensionally dual" picture of strong interaction. This generalized
amplitude can be checked in the known kinematical limits, i.e. it should reduce
to the ordinary dual amplitude on mass shell, and to the nuclear structure
function when t=0. We fix the Q^2-dependence in M-DAMA by comparing the
structure function F_2, resulting from it, with phenomenological
parameterizations. The results of M-DAMA are in qualitative agreement with the
experiment in all studied regions, i.e. in the large and low x limits as well
as in the resonance region.
