The basic idea is that you maintain a running dialogue with Iran offering carrots in exchange for verifiable steps at disarmament, while simultaneously maintaining a running dialogue with America's main allies and the other major powers about ratcheting-up Iran's diplomatic and economic isolation. The idea is to ensure that the United States is consistently the reasonable party, consistently the one prepared to strike a deal, and therefore that international diplomatic momentum remains on our side.First off, the obvious: neither of these sensible options will be pursued while Bush is in office, nor would the Iranians trust an American initiative coming from this White House. So this discussion really is the definition of academic until January 2009.
Among sensible people this is one major school of thought. The other, represented by Flynt Leverett's ... holds that we should be aiming at a "grand bargain" to resolve all the outstanding bilateral issues. ... they think this is "not practical." Leverett, by contrast, thinks it's not practical to separate the issues.
That said, I think the piecemeal approach is the preferable one here. Neither side is particularly trustworthy to the other, so before you can negotiate some kind of big-bang, all-encompassing solution -- as preferable as that might be to both sides in theory -- you need some trust-building steps in the interim. I would say as a first step Iran should comply fully with the IAEA inspectors (which would not, yet, mean they have to change their nuclear program in any way, much less abandon it) and the US should make a pledge not to attack Iran and to pursue these issues diplomatically.
Leverett has a point, however: the Iranians don't want a piecemeal negotiation, because they think the Americans will agree to the stuff that most benefits them and abandon any issues that could benefit Iran. I don't have a particularly good answer to that concern, and it's a valid one from Tehran's point of view.