If I recall correctly, the official reports state that US has stationed something like 160000 (accurate numbers are of course a military secret) in Iraq alone, and even then there seems to be difficulties (whether it is financial or simply lack of volunteers) in finding more.
Iran has a population base of roughly 69 million, of which 15-64 year old males make up 24.1 million. An ad hoc assumption yes, but also somewhat believeable would be to divide the number by two to reach the theoretical number of men who could participate war time actions simply on the age grounds. That would make around 12 million soldiers. However, not all of these would be seen in the front lines and not all of them are in a physical shape of being able to do military service. But still this is a lot of people to contain in a ground war.
I would suppose that either US reinstates the draft or has a huge air-to-ground campaign if there is a war between US and Iran. Air power is the only part of arms where Iran cannot match US. But I suppose also that Iran has a healthy supply of modern Russian SAMs, which will lead to some casualities by the USAF.
In the end that Iran would be ruined for a decade or two, but nothing else would happen, as the extremist Islamists would probably gain even more foothold during the campaign. A huge waste of ordnance and kerosine from my point of view for no good reason.
Mika
