In an event touted by President George W. Bush as a sign of U.S. success in Iraq but tinged with evidence of political friction and threats bubbling below the surface, U.S. forces Monday handed control of security in Anbar province to the Iraqis.

The U.S. military also said that Iraq’s government plans to take control Oct. 1 of more than 50,000 mainly Sunni Arab fighters known as the Sons of Iraq and allied with U.S. forces in Baghdad.

Taken together, the developments represent a major shift that will test the Shiite-led government’s willingness to support Sunni-led efforts considered key to sustaining relative calm in Iraq and fostering reconciliation.