  We perform a general analysis on the possibility of obtaining metastable
vacua with spontaneously broken N=1 supersymmetry and non-negative cosmological
constant in the moduli sector of string models. More specifically, we study the
condition under which the scalar partners of the Goldstino are non-tachyonic,
which depends only on the Kahler potential. This condition is not only
necessary but also sufficient, in the sense that all of the other scalar fields
can be given arbitrarily large positive square masses if the superpotential is
suitably tuned. We consider both heterotic and orientifold string
compactifications in the large-volume limit and show that the no-scale property
shared by these models severely restricts the allowed values for the
`sGoldstino' masses in the superpotential parameter space. We find that a
positive mass term may be achieved only for certain types of compactifications
and specific Goldstino directions. Additionally, we show how subleading
corrections to the Kahler potential which break the no-scale property may allow
to lift these masses.
