  Let $A$ be an abelian variety defined over a global field $F$ of positive
characteristic $p$ and let $\calf/F$ be a $\Z_p^{\N}$-extension, unramified
outside a finite set of places of $F$. Assuming that all ramified places are
totally ramified, we define a pro-characteristic ideal associated to the
Pontrjagin dual of the $p$-primary Selmer group of $A$, in order to formulate
an Iwasawa Main Conjecture for the non-noetherian commutative Iwasawa algebra
$\Z_p[[\Gal(\calf/F)]]$ (which we also prove for a constant abelian variety).
To do this we first show the relation between the characteristic ideals of
duals of Selmer groups for a $\Z_p^d$-extension $\calf_d/F$ and for any
$\Z_p^{d-1}$-extension contained in $\calf_d\,$, and then use a limit process.
