BAGHDAD - In darkness and dressed in black, the US and Iraqi special operations commandos navigated the dense urban neighborhood here and approached a house they believed to be a hide-out for two brothers suspected of carrying out assassinations and car bombings.

As the Iraqis bashed in the door, the sound of shattered glass and screams pierced the nighttime stillness. The Americans, having spent years taking charge on such missions, waited outside until the house was secure.

The important thing, a US sergeant said after the raid, is that the Iraqis took the lead on this operation. He spoke on the condition that he be identified only by rank to comply with the ground rules allowing a reporter access to a US Army Special Forces unit. “They are the ones doing the dirty work,’’ he said.

But Iraqi and US commanders worry that this crucial military legacy of the war may be at risk now that US forces are withdrawing this year under an agreement between the countries.

Americans say the Iraq Special Operations Forces, deliberately balanced with the country’s main sects and ethnicities, are more capable than the Iraqi Army and may be critical in preventing a resilient insurgency from exploding into a sectarian civil war.

Even as few Iraqi politicians are willing to admit publicly that they need US help, Iraqi soldiers say that US troops must stay longer to continue training and advising.

“The Americans need to stay because we don’t have control over our borders,’’ said Major General Fadhel al-Barwari, commander of the Iraq Special Operations Forces.

The commandos make up a tight-knit community where relationships between Iraqis and Americans are especially strong, having been nurtured over multiple deployments. In some cases, the Americans here are on their eighth or ninth rotations.

The senior Iraqi military leaders have advised Prime Minister Nouri al-Maliki that some troops should stay.

Even though combat has officially been declared over, Iraq still looks like a war to the Special Operations units scattered around the country.

“Yeah, anytime a guy’s got a loaded gun and he’s going out at midnight in a helicopter, you’ve got to treat it that way,’’ said a US Army Special Forces major. Even so, he said, the risks of such work have diminished greatly. “It’s been awhile since we’ve gotten in a good firefight,’’ he said.

As the major spoke at a picnic table in Victory Base Complex, the vast US complex near the Baghdad airport, several US helicopters took off nearby, ferrying a team of Iraqi and US Army Special Forces troops on their way to capture a Shi’ite militiaman suspected of firing rockets at a US base.

US Special Operations units have been training and equipping an Iraqi counterterrorism force almost from the beginning of the war in 2003. Barwari was made to do push-ups eight years ago by some of the Americans who still advise his unit. Today he directs near-nightly raids with the help of the Americans.

Barwari, whose relationship with the US military began in 1991 in northern Iraq, benefited greatly from America’s war here, and in its closing days he frets about what will become of his country without the US troops.

If Americans stay, he said, “He won’t be fighting beside me, but he will give us air support.’’

“There are many things we don’t have knowledge about,’’ he added.

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