Double
ionization of atoms in strong laser pulses is discussed by use
of a simplified atomic model. Each electron is
allowed to move along
the lines indicated by the positions of the Stark saddles when the
phase of the field changes. The effective two dimensional model
resembles to a large extend the known 1+1 dimensional aligned electrons
model, but enables correlated escape of electrons with equal momenta --
the phenomenon observed experimentally. The time-dependent solution of
the Schrodinger equation allows us to discuss in detail the time
dynamics of the
ionization process, formation of electronic wavepackets
and the development of the final momenta distribution. In particular,
we are able to distinguish between
sequential double ionization, where
electrons escape during different half-cycles of the pulse, and
non-sequential one, where they escape during the same half-cycle. We
consider the dependence of the measurable quantities on the absolute
phase of the light pulse.