The Financial Times reports that "Iran is ready to help the US stabilise Iraq if Washington were to present a timetable for withdrawing its troops from the country, Tehran's top security official [Ali Larijani, head of the Supreme National Security Council] said yesterday" (Roula Khalaf and Najmeh Bozorgmehr, "Iran Ready to Work with US on Iraq," 30 September 2007).
Why doesn't Washington take Iran's offer? Because the offer is to help Washington withdraw from Iraq, leaving a government friendly to Iran there. That is the last thing Washington wants, in fact, which is why it has not and will not take it. What Washington wants, instead, is to ensure that Iraq won't fall into the hands of Iran after it leaves -- hence the reluctance to withdraw any time soon.
What do leftists say about the offer? Urge Washington to take it? Only some do. Again, there is no coherence on the Left. Herein lies the problem. Only if Washington accepts Iran becoming a regional power, potentially capable of achieving hegemony over Iraq after US withdrawal, will it withdraw from Iraq. But some leftists have trouble accepting Iran becoming such a regional hegemon -- that's subimperialism or perhaps even imperialism in their opinion. So, there is no strong counter-discourse to the notion that "we can't let Iran have Iraq."