  S. Weinberg pointed out a way to introduce a cosmological term by modifying
the theory of gravity. This modification would be justified if the Einstein
equations with the cosmological term could be obtained in the classical limit
of some physically satisfied quantum theory of gravity. We propose to consider
quantum geometrodynamics in extended phase space as a candidate for such a
theory. Quantum geometrodynamics in extended phase space aims at giving a
selfconsistent description of the integrated system ``the physical object (the
Universe) + observation means'', observation means being represented by a
reference frame. The Lambda term appears in classical equations under certain
gauge conditions and characterizes the state of gravitational vacuum related to
a chosen reference frame. The eigenvalue spectrum of Lambda depends on a
concrete cosmological model and can be found by solving the Schrodinger
equation for a wave function of the Universe. The proposed version of quantum
geometrodynamics enables one to make predictions concerning probable values of
the Lambda term at various stages of cosmological evolution.
