  A three-orbital itinerant-electron model involving d_{xz}, d_{yz} and d_{xy}
Fe 3d orbitals is proposed for iron pnictides towards understanding the (\pi,0)
ordered magnetism and magnetic excitations in these materials. It is shown that
this model at half filling yields a gapped (\pi,0) magnetic state with high
degree of robustness and stability, and simultaneously reproduces several
experimentally observed features such as the electronic structure, spin
excitations, as well as the ferro orbital order between the d_{xz} and d_{yz}
orbitals.
