First, get out of Iraq (in full force) in the next 12-18 months.
That's not "reductions starting in 18-24 months", that's "the last marine steps on the last US plane leaving Baghdad in 18 months".
And now that's changed from "out of Iraq in 18 months" to "start thinking about reductions in a year or so".
Do you see why I'm finding your argument confusing and contradictory?
Reality is that no such reduction is going to occur and, indeed, the wheels are in motion for tens of thousands of additional US troops to go to Iraq.
Further, the experience of Iraq so far tells us that they'll end up staying there.
Any budget-balancing hypothesis that relies on any reduction of materiel committed to Iraq is doomed from the outset.