There are no solutions yet to longstanding problems like who — the American forces, or the Iraqis’ own anemic logistics system — will supply the fuel required to keep Iraqi Humvees and troop-carrying trucks running, at a time when the American supply chain will face new strains in supporting thousands of additional American troops.

Image In August, an Iraqi police officer guarded a Baghdad home as Iraqi police and American soldiers searched it. Credit... Johan Spanner for The New York Times

The plan gives a central role to the National Police, viewed as widely infiltrated by Shiite militias and, despite an intensive American retraining program, still suspected of a strongly Shiite sectarian bias. One American officer said that the National Police commanders have been “dragging their feet” over their role in the new plan and that they could seriously compromise the operation.

Against those concerns, American officers cite several factors they believe will lend impetus to the new offensive. The five additional brigades of American troops committed by President Bush — approximately 21,500 American soldiers, about 80 percent of them to be deployed in Baghdad — will roughly triple the numbers of American soldiers available for ground operations, as a relatively small proportion of the new troop strength will be needed for “force protection,” the military term for troops who safeguard bases and ensure the safety of other soldiers.

Since the resignation of former Defense Secretary Donald H. Rumsfeld after the November elections, American commanders here have been more candid in acknowledging something Mr. Rumsfeld often disputed: that the commanders have had to play shell games with thinly stretched troops, and that many crucial operations, including previous attempts to secure Baghdad, have failed because troops have often been moved on to other operations, allowing insurgents and militia groups to retake areas vacated by the Americans. The new plan, the Americans say, will go a long way toward redressing that problem, at least in Baghdad.

Another positive cited by American officers is the appointment by President Bush of Lt. Gen. David H. Petraeus as the new overall American commander in Iraq, succeeding Gen. George W. Casey Jr., who will leave next month after more 30 months in command of the war. General Petraeus, who has already completed two 12-month tours in Iraq, has a reputation among officers who have served under him as an imaginative commander who enlists strong loyalties among his troops.

Many officers interviewed for this article said they still believed the tide of the war here can be reversed, with the additional troops, the focus on regaining control of Baghdad and the more consistent military strategy they said they expected from General Petraeus. The 54-year-old native of upstate New York, a marathon runner, will come to Baghdad after overseeing the Army’s reworking of its counterinsurgency manual, parts of which he redrafted himself.

American officials in Baghdad and Washington have said that they have limited time — perhaps no more than six to nine months — to show gains from the new American push before popular support erodes still further and the onset of the 2008 presidential campaign leads American politicians to push harder for a troop withdrawal. There are also questions of how long the overstretched American military can sustain the stepped-up presence here.