Gen. David H. Petraeus formally took command of American troops in Iraq on Saturday, declaring that the mission here is hard but not hopeless.

Petraeus ... will oversee 132,000 American troops currently in Iraq and thousands more on their way as part of a so-called surge that is widely considered the last, best effort to bring peace to a country increasingly riven by sectarian violence, crime and corruption.

Iraqi officials, faced with such relentless violence, seemed unsure of whether a new American commander and the new plan could clot the bloodshed. Among American military officers, General Petraeus is considered an imaginative leader with a deep understanding of Iraq's problems, culled from two tours here. But for some in Baghdad, his assumption of control looked routine.