  The stationary and highly non-stationary resonant dynamics of the
harmonically forced pendulum are described in the framework of a semi-inverse
procedure combined with the Limiting Phase Trajectory concept. This procedure,
implying only existence of slow time scale, permits to avoid any restriction on
the oscillation amplitudes. The main results relating to the dynamical
bifurcation thresholds are represented in a closed form. The small parameter
defining the separation of the time scales is naturally identified in the
analytical procedure. Considering the pendulum frequency as the control
parameter we reveal two qualitative transitions. One of them corresponding to
stationary instability with formation of two additional stationary states, the
other, associated with the most intense energy drawing from the source, at
which the amplitude of pendulum oscillations abruptly grows.
  Analytical predictions of both bifurcations are verified by numerical
integration of original equation.
  It is also shown that occurrence of chaotic domains may be strongly connected
with the second transition.
