WASHINGTON — Iraqi security forces, backed by American-led air power and hundreds of advisers, are planning to mount a major spring offensive against Islamic State fighters who have poured into the country from Syria, a campaign that is likely to face an array of logistical and political challenges.
The goal is to break the Islamic State’s occupation in northern and westernIraq, and establish the Iraqi government’s control over Mosul and other population centers, as well as the country’s major roads and its border with Syria by the end of 2015, according to American officials.
Iraqi and Kurdish forces have made inroads in recent weeks in securing territory threatened or captured by the Islamic State, including the Rabia border crossing with Syria, the oil refinery in Baiji north of Baghdad, the northern town of Zumar, and Jurf al-Sakhar southwest of Baghdad.
But the major push, which is being devised with the help of American military planners, will require training three new Iraqi Army divisions — more than 20,000 troops — over the coming months.
“It is a balance between letting them develop their own plan and take ownership for it, and ensuring that they don’t stretch themselves too far and outpace their capability,” said one United States military official, who asked not to be identified because he was discussing war planning.
Though the United States began to carry out airstrikes to protect Erbil in August, the longer-term campaign plan has remained under wraps. Now that the planning has advanced, more than a dozen Iraqi and American officials provided details about a strategy that is certain to become increasingly visible.
The basic strategy calls for attacking fighters from the Islamic State, also known as ISIS or ISIL, with a goal of isolating them in major strongholds like Mosul.
That could enable Iraqi troops, Kurdish pesh merga units and fighters that have been recruited from Sunni tribes to take on a weakened foe that has been cut off from its supply lines and reinforcements in Syria, which are subject to American airstrikes.
To oversee the American military effort, a new task force is being established under Lt. Gen. James L. Terry, who oversees Army forces in the Middle East and who will operate from a base in Kuwait. Maj. Gen. Paul E. Funk II will run a subordinate headquarters in Baghdad that will supervise the hundreds of American advisers and trainers working with Iraqi forces.
As the push to train Iraq’s military gathers momentum, the American footprint is likely to expand from Baghdad and Erbil to additional outposts, including Al Asad Air Base in Iraq’s embattled Anbar Province in the west, and possibly Taji, 20 miles north of Baghdad.
The effort to rebuild Iraq’s fighting capability faces hurdles, including the risk that the Islamic State will use the intervening months to entrench in western and northern Iraq and carry out more killings.
The United States currently does not plan to advise Iraqi forces below the level of a brigade, which in the Iraqi Army usually has some 2,000 troops. Nor is it clear under what circumstances the White House might allow American advisers to accompany Iraqi units on the battlefield or to call in airstrikes, as Gen. Martin E. Dempsey, the chairman of the Joint Chiefs of Staff, has indicated might be necessary.
Iraq’s recent history suggests that such a battlefield advisory role is likely to be needed. Iraqi forces faltered during their 2008 offensive against Shiite militias in Basra until American commanders sent their troops to advise Iraqi forces below the brigade level and facilitate airstrikes.
As the plan stands now, no American agency has been assigned to train Iraq’s police, although they will be responsible for protecting areas that have been cleared by the army.
Iraq’s Shiite militias, some of which have been supported by Iran, pose another obstacle. Antony J. Blinken, President Obama’s deputy national security adviser, said last week that it was important that the Shiite militias be withdrawn, disband or have their members integrated into Iraq’s security forces.
But Fuad Masum, the Iraqi president, has suggested that the militias could be needed until the Islamic State was thoroughly defeated.
A major challenge will be synchronizing the Iraqi campaign with the American effort to train the beleaguered moderate Syrian opposition. The Pentagon’s program to train 5,000 Syrian rebel fighters a year in Saudi Arabia and Turkey has yet to get underway, which raises the possibility that Islamic State fighters could be pushed back into Syria well before there is a trained and equipped Syrian rebel force to oppose them.
Another constraint is self-imposed. Military officials say the White House has limited the number of United States advisers, analysts and security personnel in Iraq to 1,600. There were 1,414 troops in Iraq as of Friday, about 600 of whom were acting in advisory roles from joint operations centers in Baghdad and Erbil, and at division and higher headquarters.
A White House spokesman, Alistair Baskey, said the figure was not a limit, just the number of troops required for the current missions. One senior United States official, who asked not be identified because he was discussing internal planning, said it was likely that the number would need to be raised. Army planners have drafted options that could deploy up to an additional brigade of troops, or about 3,500 personnel, to expand the advisory effort and speed the push to rebuild the Iraqi military.
The Iraqi military has been active in recent weeks, but these operations have taken a toll on its forces. United States officials say that the initial force they are planning to advise consists of only nine Iraqi brigades and three similar Kurdish pesh merga units — roughly 24,000 troops.
The counterattack plan calls for at least doubling that force by adding three divisions, each of which could range from 8,000 to 12,000 troops.
The United States is relying on allies to augment American trainers. Australia, Canada and Norway have committed several hundred special forces to one or more of the training or advisory missions, a senior United States military official said.
A parallel effort calls for establishing new national guard brigades in each of Iraq’s 18 provinces — units that would report to the local governors and have the primary responsibility for securing those areas after the Iraqi Army has mounted its
The national guard initiative has been promoted by American officials as a way for Sunnis in western and northern Iraq to play a major role in defending their territory, which would ease sectarian frictions.
But the Iraqi Parliament has yet to enact legislation to establish the brigades, which would still need to be trained and equipped.
As a result, a “bridge” policy would be needed so that the Iraqi government, with American help, could work directly with Sunni tribes in the meantime, Mr. Blinken said at a conference hosted by the Carnegie Endowment for International Peace last week.
General Dempsey said Friday that ISIS’ recent gains in Anbar show “why we need to expand the train, advise and assist mission into” Anbar Province.
A senior United States official said that much of this bridging initiative has yet to be defined. But an early test is expected to unfold soon in Anbar, where about 5,000 Sunni tribesmen could join the fight against the Islamic State in a replay of the pivotal American effort in 2007 to enlist Sunni tribal leaders to turn against Al Qaeda’s affiliate in Iraq, the forerunner of the Islamic State.
Overcoming Sunni wariness of the Shiite-led government in Baghdad will be challenging, American officials said.
James M. Dubik, a retired three-star Army general who oversaw training of the Iraqi military during the surge in 2007 and 2008, said the most critical part of the campaign would be the effort to win the allegiance of Iraqis after the Islamic State is routed.
“Behind it has to come some reasonably legitimate, evenhanded and nonsectarian governance over those areas that are taken back from ISIS,” he said.
Even if the overall Iraqi plan succeeds by the end of 2015, American officials say, pockets of resistance could remain. American commanders acknowledge that the effort to defeat ISIS will be lengthy.
“This is not going to happen in three weeks, a month, two months,” Gen. Ray Odierno, the Army chief of staff and a former top commander in Iraq, told CNN on Wednesday. “It’s a three- to four-year effort.”