  An approach for a Poincar\'e covariant description of nuclear structure and
of lepton scattering off nuclei is proposed within the relativistic Hamiltonian
dynamics in the light-front form. Indeed a high level of accuracy is needed for
a comparison with the increasingly precise present and future experimental data
at high momentum transfer. Therefore, to distinguish genuine QCD effects or
effects of medium modified nucleon structure functions from conventional
nuclear structure effects, the commutation rules between the Poincar\'e
generators should be satisfied. For the first time in this paper a proper
hadronic tensor for inclusive deep inelastic scattering of electrons off nuclei
is derived in the impulse approximation in terms of the single nucleon hadronic
tensor. Our approach is based : i) on a light-front spectral function for
nuclei, obtained taking advantage of the successful non-relativistic knowledge
of nuclear interaction, and ii) on the free current operator that, if defined
in the Breit reference frame with the momentum transfer, $\bf q$, parallel to
the $z$ axis, fulfills Poincar\'e covariance and current conservation.
  Our results can be generalized : i) to exclusive processes or to
semi-inclusive deep inelastic scattering processes; ii) to the case where the
final state interaction is considered through a Glauber approximation; iii) to
finite momentum transfer kinematics.
  As a first test, the hadronic tensor is applied to obtain the nuclear
structure function F$_2^A$ and to evaluate the EMC effect for $^3He$ in the
Bjorken limit.
  Encouraging results including only the two-body part of the light-front
spectral function are presented.
