  A new mechanism of adjustment of vacuum energy down to the observed value
from an initially huge one is considered. The mechanism is based on a very
strong variation of the gravitational coupling constant in very early universe.
The model predicts that the non--compensated remnant of vacuum energy changes
very slowly at late stages of the cosmological evolution and is naturally close
to the observed one. Asymptotically the effective vacuum energy tends to a
negative value, so the cosmological expansion should stop and turn into
contraction. There remains the problem of introduction of the usual matter into
the model and therefore realising realistic cosmology.
