  Near a bifurcation point a system experiences critical slowing down. This
leads to scaling behavior of fluctuations. We find that a periodically driven
system may display three scaling regimes and scaling crossovers near a
saddle-node bifurcation where a metastable state disappears. The rate of
activated escape $W$ scales with the driving field amplitude $A$ as $\ln W
\propto (A_c-A)^{\xi}$, where $A_c$ is the bifurcational value of $A$. With
increasing field frequency the critical exponent $\xi$ changes from $\xi = 3/2$
for stationary systems to a dynamical value $\xi=2$ and then again to
$\xi=3/2$. The analytical results are in agreement with the results of
asymptotic calculations in the scaling region. Numerical calculations and
simulations for a model system support the theory.
