  In the framework of four-band model of superconductivity in iron arsenides
proposed by Barzykin and Gor'kov we analyze the gap ratios on hole - like and
electron - like Fermi - surface cylinders. It is shown that experimentally
observed (ARPES) gap ratios can be obtained only within rather strict limits on
the values of pairing coupling constants. The difference of T_c values in 1111
and 122 systems is reasonably explained by the relative values of partial
densities of states. The multiple bands electronic structure of these systems
leads to a significant enhancement of effective pairing coupling constant
determining T_c, so that high enough T_c values can be achieved even for the
case of rather small intraband and interband pairing interactions.
