It's hard to predict. The first instinct says no. US and Europe has mostly preferred proxy wars to weaken their enemy and they might threaten Iran but won't get directly involved. Getting directly involved may mean losing their middle east bases. There are also talks of unofficial agreement among the middle eastern nations that US would not be directly involved and US bases in Iraq, Kuwait, Baharain, Qatar, UAE, Syria, Jordan and Saudi Arabia would be spared. If US gets involved, Iran would have no reason not to bomb those bases. Iran is said to be isolated in the reason with all of its neighbors against Uranium enrichment plans. It might force Iran to strike a deal with US before the need of US involvement in conflict. As, US is trying to solve it diplomatically, UK and France might get involved earlier so US could still play as a good cop.