  We study the early-time behavior of isotropic and homogeneous solutions in
vacuum as well as radiation-filled cosmological models in the full, effective,
four dimensional gravity theory with higher derivatives. We use asymptotic
methods to analyze all possible ways of approach to the initial singularity of
such universes. In order to do so, we construct autonomous dynamical systems
that describe the evolution of these models, and decompose the associated
vector fields. We prove that, at early times, all flat vacua as well as general
curved ones are globally attracted by the "universal" square root scaling
solution. Open vacua, on the other hand show in both, future and past
directions a dominant asymptotic approach to horizon-free, Milne states that
emerge from initial data sets of smaller dimension. Closed universes exhibit
more complex logarithmic singularities. Our results on asymptotic stability
show a possible relation to cyclic and ekpyrotic cosmologies at the passage
through the singularity. In the case of radiation-filled universes of the same
class we show the essential uniqueness and stability of the resulting
asymptotic scheme, once more dominated by $t^{1/2}$, in all cases except
perhaps that of the conformally invariant Bach-Weyl gravity. In all cases, we
construct a formal series representation valid near the initial singularity of
the general solution of these models and prove that curvature as well as
radiation play a subdominant role in the dominating form. A discussion is also
made on the implications of these results for the generic initial state of the
theory.
