If the UN approves striking Iran, then it must be serious! So yes, I'd support it 100%. Without UN support, however, no; we'd just make it look like another clash of civilizations: it's bad enough as it is right now.
Of course I'd be all for it. If the UN aurthorized it, even though the UN security council is somewhat dominated by veto wielding members such as the USA, I'd still be 100% the UN's choice and operations.
However I think some reforms have to be made to the UN security council as in taking away all 5 veto wielding members, veto away. I'm sick of all those nations ability to nurf UN dessions.