Muhsin Khidr al-Khafaji, number 48 on the US list of most-wanted Iraqis, turned himself in to Iraqis who then handed him over to US forces, the official said.
Muhsin was the Baath Party chairman for al-Qadisiyah governorate and was the three of diamonds in the deck of cards identifying the United States' most wanted.
If confirmed, al-Khafaji's arrest would mean that 43 of the 55 Iraqis on the list have been caught or killed so far.
Izzat Ibrahim al-Duri, Saddam Hussein's former deputy, is the highest-ranking former government official still at large.
The US accuses al-Duri of being one of the key organisers of resistance attacks around Samarra and Tikrit.
Meanwhile, troops from the Fourth Infantry Division have captured 11 Iraqis suspected of involvement in anti-coalition activities, the military said.
Six suspected resistance fighters were seized in Samarra on Saturday without incident, the Central Command announced.
Five others believed to be weapons dealers were arrested outside the town of Mukdadiyah on the same day.
Two AK-47 assault rifles, two 9mm pistols, four 9mm ammunition magazines, and nine AK-47 ammunition magazines were confiscated from them.