  To perform a local orbital analysis of electronic and magnetic interactions,
we construct the Wannier functions (WFs) of the Fe $3d$ orbitals in the parent
compound of the recently discovered iron pnictide superconductors, LaFeAsO, and
a comparison material LaFePO. Comparing the WFs for the stripe
antiferromagnetic order with those for no magnetic order, the difference is a
significant spreading (``{\it de}localization'') of specifically the $d_{xy}$
and $d_{xz}$ (but not $d_{yz}$) WFs, where parallel Fe spins lie along the $x$
direction. The WF basis gives a tight-binding representation of the first
principles, density functional based Fe-derived bands. Comparing hopping
parameters, it is found that changes due to stripe antiferromagnetism, even if
it is weak, enables more isotropic hopping involving spin-majority electrons in
the Fe $3d_{xz}$ (but not the $3d_{yz}$) orbital. This change,
counterintuitively, actually reinforces electronic anisotropy. Further insight
is gained by comparing the WFs of LaFeAsO and LaFePO, identifying how the
difference in WFs is related to the difference in hopping integrals and showing
how the pnictide atom is influential in forming the stripe antiferromagnetism.
Kinetic energy considerations suggest that orbital fluctuation, in addition to
spin fluctuation, may contribute to the decrease in observed ordered moment
compared to the calculated values.
