  We study relations between hydrodynamical (H) and scalar field (SF) models of
the dark energy in the early Universe. Main attention is paid to SF described
by the canonical Lagrangian within the homogeneous isotropic spatially flat
cosmology. We analyze requirements that guarantee the same cosmological history
for the SF and H-models at least for solutions with specially chosen initial
conditions and we present a differential equation for the SF potential that
ensures such a restricted equivalence of the SF and H-models. Also, we derived
a condition that guarantees an approximate equivalence when there is a small
difference between energy momentum tensors of the models. The "equivalent"
scalar field potentials for linear equations of state (EOS) are found in an
explicit form, we also present an examples with more complicated EOS.
