  We study the possibility of canceling the cosmological constant in
supergravity string models. We show that with a suitable choice of
superpotential the vacuum energy may vanish with the dilaton field at its
minimum and supersymmetry broken with a large hierarchy. We derive the
condition for which the introduction of a chiral potential, e.g. the inflaton
potential, does not destabilize the dilaton field even in the region where the
scalar potential takes positive values. This allows for an inflationary
potential with the dilaton frozen at its minimum.
