Vanishing of the Cosmological Constant, Stability of the Dilaton and Inflation

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.