  Starting from the QCD Lagrangian we derive the effective action for massive
quark and antiquark at large distances, corresponding to the minimal area low
of the Wilson loop. The path integral method is used to quantize the system and
the spectrum is obtained with asymptotically linear Regge trajectories. Two
dynamical regimes distinguished by the string energy--momentum distribution are
found: at large orbital excitations ($l\gg 1$) the system behaves as a string
and yields the Regge slope of $\frac{1}{2 \pi \sigma}$, while at small $l$ one
obtains a potential-like regime for relativistic or nonrelativistic system .
The problem of relative time is clarified. It is shown that in the valence
quark approximation one can reduce the initial four-dimensional dynamics to the
three-dimensional one. The limiting case of a pure string (without quark
kinetic terms) is studied and the spectrum of the straight-line string is
obtained.
