  We analyze antiferromagnetism and superconductivity in novel $Fe-$based
superconductors within the itinerant model of small electron and hole pockets
near $(0,0)$ and $(\pi,\pi)$. We argue that the effective interactions in both
channels logarithmically flow towards the same values at low energies, {\it
i.e.}, antiferromagnetism and superconductivity must be treated on equal
footings. The magnetic instability comes first for equal sizes of the two
pockets, but looses to superconductivity upon doping. The superconducting gap
has no nodes, but changes sign between the two Fermi surfaces (extended s-wave
symmetry). We argue that the $T$ dependencies of the spin susceptibility and
NMR relaxation rate for such state are exponential only at very low $T$, and
can be well fitted by power-laws over a wide $T$ range below $T_c$.
