U.S. troops train Iraqi soldiers in 2010. After the collapse of the Iraqi army this year in the face of Islamic State forces, U.S. officials are training a smaller number of higher-quality Iraqi units to fight the jihadists. (Khalil Al-A'nei/EPA)

After learning hard lessons rebuilding foreign militaries over the past dozen years, the U.S. military is shifting its strategy against the Islamic State, choosing to train a smaller number of Iraqi soldiers rather than trying to stand up an entire army anew.

At their peak, Iraqi combat forces, painstakingly built and paid for by the United States during the last Iraq war, numbered about 400,000 troops. By the time the Islamist militant group launched its advance across northern Iraq in June, the Iraqi forces had shrunk by as much as half, depleted by years of corruption, absenteeism and decay.

When the Islamic State completed its seizure of the city of Mosul, four Iraqi army divisions and another from the federal police had disappeared, shrinking the original combat force to as few as 85,000 active troops, according to expert estimates.

As the Obama administration scrambles to counter the Islamic State, commanders have decided against trying to rebuild entire vanished divisions or introduce new personnel in underperforming, undermanned units across the country, according to U.S. officials. Rather, the officials said, the hope is to build nine new Iraqi army brigades — up to 45,000 light-infantry soldiers — into a vanguard force that, together with Kurdish and Shiite fighters, can shatter the Islamic State’s grip on a third of the country.

“The idea is, at least in the first instance, to try and build a kind of leaner, meaner Iraqi army,” said a senior U.S. official, who, like others, spoke on the condition of anonymity to discuss planning.

Kurdish peshmerga forces clashed with Islamic State insurgents south of the oil-rich city of Kirkuk in Iraq late on Tuesday. (Reuters)

The development of a spearhead force is unlikely to address the larger decay across Iraq’s security forces and institutions, a more complex, deeply rooted phenomenon that undermines the country’s stability. The force is also insufficient on its own to retake strategic cities such as Mosul.

But U.S. officials and others said the training of a smaller number of high-quality units could enable Iraqi security forces to make significant headway against the Islamic State — supplemented eventually, U.S. officials hope, by a new “national guard” that could bring an array of armed groups operating across Iraq under provincial government control.

“Before the Mosul crisis, we were living in a fantasy,” said Hakim al-Zamili, head of the Iraqi parliament’s security and defense committee. “We thought the army could defend the country. We trusted them. But what happened revealed the truth to us.”

The Obama administration’s plan for repairing some of Iraq’s most serious military failings appears unlikely to change with Defense Secretary Chuck Hagel’s impending departure. Inside the Pentagon, Hagel was known as being closer to reform programs and budgetary initiatives than to the military campaign against the Islamic State.

U.S. officials blame former Iraqi prime minister Nouri al-

Maliki for the decline in the quality of Iraqi forces after the U.S. military withdrawal in 2011. They say the Shiite leader assigned commanders on the basis of sectarian loyalty, diminishing military capabilities and undermining morale.

Under corrupt leadership, payrolls were padded with “ghost soldiers” and payments issued for troops long dead — a system that not only resulted in undermanned military units but contributed to the difficulty of assessing the size and strength of the security forces.

According to Michael Knights, a fellow with the Washington Institute for Near East Policy who has been assembling a detailed analysis of remaining Iraqi military units, army brigades that were supposed to comprise as many as 4,000 men have regularly included fewer than half that number.

“There was a huge disconnect” between the military Iraq had on paper and what it looked like in reality, a senior U.S. defense official said, speaking on the condition of anonymity.

The problems laid bare this summer were a surprise even to those involved in the 2003-2011 initiative to rebuild Iraq’s military, an undertaking that cost more than $25 billion. While an even lengthier effort in Afghanistan has paid dividends in the fight against the Taliban, Afghan forces still lack advanced military capabilities and are suffering high battle casualties.

The Obama administration has been encouraged by the initial reforms that Iraqi Prime Minister Haider al-Abadi, who took over from Maliki in August, has made. This month, Abadi replaced more than 20 senior military commanders. He has also eliminated the commander-in-chief office that Maliki had established to tighten his grip on the military. How far Abadi — seeking to keep a fragile national unity government intact — can push those reforms is unknown.

Even when the nine army brigades complete their two-month training, those more competent troops will represent a modest share of the larger Iraqi army, which Knights estimated comprised just 36 active brigades after the defeat in Mosul. The United States also plans to train three brigades of Kurdish peshmerga forces.

“Whether [the training plan] is adequate or not, it might be what’s possible right now,” Knights said.

Retired Army Lt. Gen. Jim Dubik, who headed the U.S. training of Iraqi forces from 2007 to 2008, said Iraqi troops would need to progressively clear militant-held territory, as U.S. forces did during President George W. Bush’s troop surge, but without a large U.S. ground force for support.

“It’s possible, but it will take longer,” Dubik said.

The vanguard force, for instance, would be smaller than what is required to retake Mosul, where hostility toward Baghdad’s Shiite-led government has long fueled support for insurgents. Officials hope an offensive to reclaim the city can occur in the first quarter of 2015. Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, has said that three divisions, or roughly 80,000 troops, would be needed to attempt an assault on Mosul.

U.S. officials are backing a

longer-term Iraqi plan to restructure the army, transforming a force that was supposed to comprise 14 to 15 divisions into one of seven to eight slightly larger-than-normal divisions: one armored, two mechanized and five light infantry, the senior defense official said. That is in addition to Iraqi special-forces troops who have borne the brunt of the fighting this year.

The success of plans to create a smaller army that is focused on Iraq’s external defense will hinge on a second initiative, to build a “national guard” to provide security in Iraqi cities and towns.

Zamili said his committee was preparing to examine a draft of the law needed to establish the guard. An early copy of the draft law that was leaked to the Iraqi media showed the program would seek to recruit former officers from the Saddam Hussein-era military, some of whom are believed to support the Islamic State.

The initiative echoes a program launched in 2006-2007, when U.S. forces helped organize Sunni tribesmen in western Iraq, and then across the country, to fight al-Qaeda. But plans to secure a lasting Sunni buy-in failed when promised jobs did not materialize for many of the tribal fighters, fueling resentment against Baghdad. Tribesmen cooperating with Baghdad also have been widely targeted by militants.

This time, U.S. officials say, Abadi is working to demonstrate support for Sunnis. “The national guard concept is designed not to repeat that mistake,” the first U.S. official said.

Another senior U.S. official, also speaking on the condition of anonymity, said that the Iraqi government has integrated a “couple hundred” tribesmen into Iraqi forces as part of a “bridging solution” before the national guard can be established.

Sheik Naim al-Gaoud, a tribal elder from Anbar, expressed tentative support for the program: “We must have guarantees we will not be abandoned.”

U.S. officials hope the program will eventually absorb Kurdish peshmerga forces and at least some Shiite militiamen. The goal is ambitious given the likely reluctance of Kurdish or Shiite militia leaders to cede power to the central government, and the obstacle of first getting the proposal through Iraq’s fractious parliament.

Fuad Hussein, a senior official in the Kurdistan Regional Government, said Iraqi Kurdish leaders are open to including Kurdish troops in a national guard but doubt that the plan can take root in the midst of the current crisis. “The idea is not bad, but how are you going to implement that?” he said.

As the United States deepens its involvement, the growing role played by Iranian-backed Shiite militias remains a source of discomfort for U.S. officials.

Groups such as Asaib Ahl al-Haq and the Badr Brigade helped fuel Iraq’s sectarian bloodshed in the years after the U.S. invasion in 2003. Although militia activity subsided in recent years, the fighters have returned in force to battle the Islamic State.

The militias have played a pivotal part in some of the few Iraqi successes. The militiamen, who analysts estimate as numbering in the tens of thousands, appear to be coordinating with Iraqi security forces but are not under the government’s command.

“We are watching it closely, and we are also sending very strong signals to Abadi that it doesn’t obviously serve Iraq’s interest to have militias going on rampages against Sunni civilians,” the first official said. “He gets it.”

Rights groups have been increasingly alarmed by reports of kidnappings and sectarian attacks by militiamen, including an August massacre in a Sunni mosque that Human Rights Watch blamed on Iraqi forces and Shiite militiamen.

“Unless these militias are reined in, it is likely that the U.S. will be perceived as supporting the growing sectarian divide in Iraq,” said Sarah Margon, the group’s Washington director.

For now, Abadi and the United States both need the militias to make up for shortcomings in the Iraqi military, said Ahmed Ali, an analyst with the Institute for the Study of War in Washington. But Iraqi officials say the new prime minister is worried about what happens “the day after” — if and when the fight against the Islamic State is won.

Cunningham reported from Baghdad. Mustafa Salim contributed to this report.