  The Hamiltonian theory of a relativistic string is considered in a specific
reference frame in terms the diffeo-invariant variables. The evolution
parameter and energy invariant with respect to the time-coordinate
transformations are constructed, so that the dimension of the kinemetric group
of diffeomorphisms coincides with the dimension of a set of variables whose
velocities are removed by the Gauss-type constraints in accordance with the
second Noether theorem. This coincidence allows us to solve the energy
constraint, and fulfil Dirac's Hamiltonian reduction.
