I'll tell you exactly what our government is thinking: Iraq and Afghansitan must be secure, progressive, and secular democracies before anything major can happen in Iran. Any kind of major upheaval in Iran may cause turmoil in the region if Iraq and Afghanistan aren't established and independent democratic countries. And due to history of problems in Iran, it's best to just "allow the regime to collapse".
But, anyone who thinks the regime is just going to "collapse", is living in outerspace. The regime has a fiercly loyal 15% backing - volunteer basiji who'd kill themselves before they'll allow demonstrations in the streets, hezbullah who are well-funded by the regime and know they will disappear if the regime goes, neighboring countries that fear a secular democratic Iran will be horrendous for their own regimes, revolutionary guards that owe alligance to the regime, Bazaris who receive their bread and butter from the regime, international nations [europeans, russians, japanese, chinese who are only worried about Iran's oil, and the media who simply don't give a flop - since this is a pro-Freedom movement.
Unless there is mass covert backing any form of change in government is impossible. The reigning hard-liners will never succumb, nor will they ever reform.
My Iranian friend put it best when he said "The Mullahs are not like the Shah, they don't think morally, ethically, or principally; they will kill each and every individual that threatens their stay in power." <--- in reference to the Shah refusing to allow executions of most of the Islamists in the country.