  This work examines a relativistic model for the observed inhomogeneities of
the large scale structure where the hypothesis that this structure can be
described as being a self-similar fractal system is advanced. The concept of
hierarchical clustering is identified with a fractal distribution and the
problems raised by the use of fractal ideas in a relativistic model are
discussed, as well as their relations to the Copernican and Cosmological
Principles. Voids, clusters and superclusters of galaxies are assumed to be
part of a smoothed-out fractal structure described by a Lemaitre-Tolman
solution. The basic concepts of the Newtonian model presented by Pietronero
(1987) are reinterpreted and applied to this inhomogeneous curved spacetime.
This fractal system is also assumed to have a crossover to homogeneity which
leads to a "Swiss cheese" type model, composed by an interior Lemaitre-Tolman
metric and an exterior dust Friedmann solution. The Darmois junction conditions
between the two spacetimes are calculated, and the observational relations
necessary to compare the model with observations are obtained for the interior
region. The differential equations of the interior spacetime are set up and a
numerical strategy is devised for finding particular Tolman solutions
representing a fractal behaviour along the past light cone.
