BOOST IN IRAQ TROOPS A SHIFT FOR U.S.

WASHINGTON — Pentagon officials have warned for months that Islamic State, the Sunni extremist group that President Obama initially dismissed as a “JV team,” is nimble, aggressive and unlike any previous terrorist group.

On Wednesday, alarmed by the militants’ latest battlefield successes, the White House tacked sharply and announced the deployment of an additional 450 U.S. military advisors and support troops to help bolster Iraq’s beleaguered security forces, including local Sunni tribes.

The boost in troops, the first since November, will expand the U.S. footprint to a fifth base, close to insurgent strongholds in Anbar province. U.S. military trainers already operate at four bases, although one currently lacks Iraqi trainees.

“This decision does not represent a change in mission,” Defense Secretary Ashton Carter said in a written statement, noting that U.S. troops still will be barred from conducting offensive ground combat.

But the new focus on breaking the extremists’ grip in Anbar marks a major shift in U.S. strategy and puts American troops considerably closer to the front lines.

The militants’ surprise capture last month of Ramadi, capital of Anbar, prompted a reappraisal of Pentagon planning. A fear that Islamic State fighters would entrench themselves in the city and use it as a launching pad for attacks on Baghdad, an hour’s drive away, proved a factor.

But so did White House recognition that the military approach that has evolved over the last year, a combination of intense coalition airstrikes and hit-or-miss Iraqi ground assaults, isn’t close to meeting Obama’s objective of pushing Islamic State out of Iraq.

In recent months, the Pentagon had highlighted efforts to retake the strategic northern city of Mosul, even telling reporters this spring that a U.S.-backed ground offensive was all but imminent.

That ambitious plan has been shelved indefinitely. Mosul, a city of 1 million, fell to the insurgents a year ago Wednesday and remains the largest city under strict Islamic State control. It serves as the Iraqi capital of the group’s self-declared caliphate.

Instead, U.S. officials are seeking to rekindle the socalled 2006-08 Anbar Awakening. Back then, Sunni tribal fighters paid and armed by the U.S. took on and ultimately helped defeat Al Qaeda militants, also Sunnis, who had fueled a vicious sectarian war after the 2003 U.S.-led invasion.

Pentagon spokesman Col. Steve Warren cited that model Wednesday, saying the goal is to enlist the Sunni militias to help retake Ramadi and the nearby militant stronghold of Fallouja.

“We have experience with this,” Warren said. “This is something that we have had great success with in the past and something we understand how to do.”

After huddling with Iraqi Prime Minister Haider Abadi at the Group of 7 summit in Germany early this week, Obama agreed to empower the Sunni tribes again. Abadi, a Shiite Muslim, promised to recruit and train Sunni fighters for inclusion in the regular army, a U.S. demand.

As a result, Obama ordered the Pentagon to expedite delivery of weapons and equipment not only to Iraqi government forces and allied Kurdish fighters in the north, who have received U.S. aid since last summer, but also to the tribal fighters in eastern Anbar. The central government will coordinate the deliveries.

The Shiite-dominated Iraqi army is unpopular in predominantly Sunni Anbar, where the troops are widely seen as an occupying force. The hope is that the local Sunni tribesmen, trained and armed by Americans, and with clear support from Baghdad, can again turn the tide.

Much of the effort will be run from Taqaddum air base, which became the Iraqi military operations base in eastern Anbar after the army retreated from Ramadi. Pentagon officials said U.S. troops will be sent there to advise and assist Iraqi commanders with specific battle maneuvers, coordination of units and attack planning in Anbar.

“I think this will have a fairly dramatic effect,” Brett H. McGurk, deputy assistant secretary of State for Iraq and Iran, said Wednesday during a White House conference call with reporters.

He said fighters from three tribes have assisted Iraqi army troops in western Anbar, near Al Asad air base, where U.S. troops have been based since November.

“We’ve been able, through our advise-and-assist mission, to organize the tribes, organize Iraqi forces and take back territory,” McGurk said. “That’s been a real success, and we’ve looked at that in terms of what’s worked and can we build on that, can we reinforce that.”

The White House announcement did not include plans for Apache attack helicopters or U.S. spotters on the ground to call in airstrikes, options that some hawks say are needed. But McGurk left the door open for widening the U.S. involvement.

“The president has always said he’ll consider any option that’s recommended to him,” McGurk said. “In the case of Taqaddum, we have to get on the ground, we have to develop the relationships there, work with the joint operations center, work with their plan, and then we’ll assess from there.”

The new deployment will bring the number of U.S. troops in Iraq to about 3,550.

The shift comes as militants have stepped up their use of vehicle bombs and suicide attacks, a demoralizing tactic that proved crucial in their defeat of Iraqi troops in Ramadi. The insurgents turned American-made Humvees and construction machinery into massive rolling weapons that leveled entire city blocks.

In recent months, U.S. advisors have trained Iraqi soldiers at four bases: Taji, Besmaya, Irbil and Al Asad. Although U.S. officials said more than 9,000 Iraqis have completed the training, and 3,000 more are enrolled, Al Asad has no trainees at the moment. The base is the most remote and courses were held there last month on small unit tactics and how to counter roadside bombs, officials said.

Obama has sought to thread a needle in Iraq — doing enough to hurt Islamic State but resisting pressure to launch a deeper intervention. Josh Earnest, the White House press secretary, said Wednesday that Obama wants to support the Iraqis but that he doesn’t want to “do for them what they must do for themselves.”

That’s not good enough for some critics, who decry the latest U.S. move in Iraq as too little, too late.

Mowaffak Rubaie, Iraq’s former national security advisor and now a lawmaker, urged the White House to deploy U.S. troops into combat to direct coalition airstrikes on militants in densely populated areas.

“We need him to put spotters on the ground,” Rubaie said in an email. “We need him to intensify the airstrikes and change the rules of engagement. We need him to perform more high-end counter-terrorism operations” against the militants, he said.

House Speaker John A. Boehner (R-Ohio) said Obama’s decision was “a step in the right direction” but insufficient.

“It’s clear that our training mission alone has not been enough to slow down the spread of ” Islamic State, Boehner told reporters.