Bush wants to get the Iraqi parliament to give him permission to attack Iran so he doesn't have to get permission from Congress.
The reason the White House is so hell-bent on signing a long-term agreement may have less to do with Iraq and more to do with Iran. According to press reports of the ongoing negotiations,
the Bush administration is seeking the “power to determine if a hostile act from another country is aggression against Iraq.” Ali al Adeeb, a leading member of Prime Minister Nouri al-Maliki’s Dawa party, confirmed:
The Americans insist so far that is they who define what is an aggression on Iraq and what is democracy inside Iraq…if we come under aggression we should define it and ask for help.
The administration’s request would seemingly allow the U.S. to brand Iran as an enemy of Iraq and attack Iran in the name of defending Iraq pursuant a legal obligation under the status of forces agreement.
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Since the administration is unlikely to get an Iran war authorized through Congress, it’s instead trying to sneak it through the Iraqi parliament.
http://thinkprogress.org/2008/06/11/iran-war-iraq-sofa/andTargeted Strike on Iran Nuclear Sites Under Discussion Again
http://www.mcclatchydc.com/227/story/40764.html