The document, an apparent review of the group's strategy in the Iraqi capital, was seized with videos on April 16 near Yusufiya, just southeast of Baghdad, the military said on Monday.
A translation of the undated, three-page document, whose authenticity could not be independently assessed, suggested al-Qaeda was reviewing tactics in the city, currently focused on car bombs and other guerrilla tactics.
It proposes improving its military capabilities to hold territory, in what appeared to be preparation for a civil war.
The document was mentioned in a news briefing last week at which the military also aired what it said were shots from a video promoting the leader of al-Qaeda in Iraq, Abu Musab al-Zarqawi.
A statement accompanying a translated transcript of the "Baghdad strategy" document quoted Brigadier-General Rudy Wright, a US military spokesman, as saying:
"This information confirms what the government of Iraq, coalition forces and ultimately the people of Iraq already know - that AQIZ's role only attempts to impede Iraqis in following the road to prosperity, security and national unity."
AQIZ is a US acronym for "al-Qaeda in Iraq, Zarqawi".
The statement also quoted the document as saying: "Al-Qaeda in Iraq attacks mosques and other public places to draw media attention and is having difficulty recruiting members because the people of Iraq do not support its cause."
The transcript did not include that sentence.
The US military has previously released what it says are captured documents showing dissent or disillusion in fighters' ranks.
The translation provided by the military showed the unknown author putting the strength of active fighters, referred to as mujahidin or holy warriors, at about 110 in Baghdad - 40 each in the northwest and southwest and 30 in the east.
"These are very small numbers compared to the tens of thousands of the enemy troops. How can we increase these numbers?" the document concludes.
US and Iraqi officials generally assess the number of fighters in the thousands.
The document also criticises car bombings and other "surprise attacks" that are "the main strength of the brothers in Baghdad".
Preparing for war
An element of the document not mentioned in the US statement was its urging the group to prepare to hold territory, possibly in an all-out civil war.
"The policy followed by the brothers in Baghdad is a media-oriented policy without a clear comprehensive plan to capture an area or an enemy centre," the writer says, as translated by the US military.
"This direction has large positive effects; however, being preoccupied with it alone delays more important operations such as taking control of some areas, preserving it and assuming power in Baghdad (for example, taking control of a university, a hospital, or a Sunni religious site)."
The document also raises the question of the loyalties of Sunni Iraqi troops and is critical of the Iraqi Islamic Party, the main Sunni group expected to be involved in a new, national unity government, as well as the Sunni Muslim Clerics Association, describing them as rivals for influence over the Sunni minority.