  A modification of the optimal fluctuation approach is applied to study the
tails of the free energy distribution function P(F) for an elastic string in
quenched disorder both in the regions of the universal behavior of P(F) and in
the regions of large fluctuations, where the behavior of P(F) is non-universal.
The difference between the two regimes is shown to consist in whether it is
necessary or not to take into account the renormalization of parameters by the
fluctuations of disorder in the vicinity of the optimal fluctuation.
