1. Lay down mines along the Persian gulf (Specialy Hormuz strait) to stop oil shiping. Block it aditionaly with antiship missiles. This would not last long but would for some time sky rocketed oil price.
Oil will skyrocket anyway and just like during the "tanker wars" of the 80's, America's ability to defend against ASM attack FAR outweighs Iran's ability to launch said attacks. In addition to which the US's ability to target such assets obviously exceeds Iran's ability to defend itself...
2. It can give few Bin in arms to Shia population in Iraq. iran is suporting Shia but it would be another thing if US had to face those rebels with their hands laid on Metis-M/Kornet/ igla-S. Same thing goes for Afganistan.
I think you'll find the American's ARE facing such threats already, but certainly MUCH tighter border security would have to be a factor in this war...
3. Iran is 4 times bigger country than Iraq and three times more populated witch means no ground invasion is possible while Iraq stability is in question ... that leaves only airforce option open (From neirby countries and carriers).
I don't think anyone is contemplating such an operation, however what precisely makes you think the Iranian's would last any longer than the Iraqi Army? Fact is America couldn't find ENOUGH targets during GW2 to actually strike...
4. Iran has about 2000 balistic missiles of all kinds and posible more of witch some are MIRV-ed and most of them have mutched increased accuracy (as shown during latest Iran rocket fireing) CEP aprox 200m.
On the other side US has 170 000 solders in Iraq within 30-50 major bases and no country has means to defend itseld from such massive missile atack. it would be wrong to assume that US can with pre-emtive stikes destroy Irans balistic missile capability (maybe those static but vast majority are mobile) as in 1991 about 50% of USAF + special forces searched and found none of Iraq mobile SCUD lounchers during the first Gulf war.
Same thing for Afganistan as it is also irans neighbour.
Patriot missile did not show itself during the first Gulf war and US has about 700-800 Patriot PAC-3 missiles mostly of witch are not in Iraq but are intended to protect US coast from cruise missile atack besides no country in the world can repel such massive missile atack.
Arrow-2 block 3 TBMD with ability to shoot down Sahab-3 is only this year rushed in the production. So I think Irans missile potential is something not to be underestimated.
Indigenous missile systems in the Middle East don't have a particularly great record from what I've seen. They generally prove to be weapons of terror, rather than usable tactical systems.
Who exactly they are going to fire at I find interesting though. Do you think US troops and major installations in Iraq wouldn't be protected? Israel perhaps? Possibly, but you can be assured that Iran's offensive missile capabilities will be a prime target for the US attack. Personally I think the Iranians would be too busy trying to hide them, to fire too many.
As with Iraq's SCUDS, these missiles require TEL's to fire from and such are easily detected prior to launch. These missiles are also liquid fuelled, which has to be done on the TEL as I understand such things and again this takes time and is rather obvious to those who look for such things (ie: J-STARS etc).
Like Iraq, it will be a matter of how many missiles Iran can fire, before said are destroyed by American air power undertaking time sensitive targetting missions above them...
6. Iran can also lounch massive missile atacks on oil rafinery along the Pesrsian gulf with logic in mind: If US is about to blow us in stone age we just might along the proces blow up some rafineries and make war mutch more expensive besides most of the midle east countries host US bases so by helping Americans those countries might be subjected to atacks.
Again, US anti-missile capability isn't just PAC-3 Patriot and AEGIS class cruisers. It'll destroy far more missiles on the ground than will ever launch in my opinion. Hitting an oil refinery with a ballistic missile for Iran seems a bit ambitious to me. Certainly hitting many of them...
7. Most of the population in Midle east countries do not suport theirs pro-western govrements and by atacking Iran some kind of "color" revolution just might happen (that is if Iran decides not to lounch missiles on midle east countries).
Just like they rose up against the West when America attacked Iraq?
8. Imagine Al Qaida happines in the event of war and their potential to grow in cercumstances of total war.
Al Qaeda is nothing more than a terrorist organisation. They have to conduct assymetric attacks because they cannot stand up to a conventional military force. They have to run and hide when faced with modern warfare capabilities. Thinking they'll be anything else, is a bit much for me...
9. Unlike regular troops Revolutionary guard is not to be underestimated since inflitration in Iraq and Afgan is possible and they could cause quite a mess there.
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As opposed to the "Paradise" it is now? You've got 165,000 US ground forces in Iraq. I think they'd love a conventional fight right about now actually...