Baghdad ? Lt. Ryan Alexander stands thigh-deep in a dark grove of reeds and palm trees, hunting for rockets. Officially, the U.S. combat role in Iraq is ending this month, but Alexander and his platoon are under orders to keep insurgents from using the south Baghdad field as a hiding place for Katyushas.

“We’re going to be doing this as long as they tell us,” Alexander said in a near-whisper in the steamy pre-dawn air, his machine gun slung over his shoulder. Behind him, Iraqi Lt. Wassan Fadah Hussein had his handgun out and ready for action.

In the near distance came a gunshot. “Sounded like a little boom,” Alexander drawled.

The number of U.S. soldiers in Iraq dipped Tuesday to 49,700, dropping below the 50,000 threshold ahead of the end-of-the-month deadline set by President Barack Obama. But the war is not yet over for the remaining troops, who will continue to put themselves in danger on counterterror raids and other high-risk missions that aren’t called combat but can be just as deadly.

Until the end of 2011, U.S. troops will mostly focus on training Iraqi soldiers and police to take over the nation’s still-shaky security. They will counsel Iraqi officials on how to endear themselves to their citizens, whether through handing out soccer balls to kids or building irrigation systems for farmers.

But they will also still be on security patrols — like the one that Iraqi police said was hit by a roadside bomb Tuesday in the southern city of Basra, with no casualties immediately reported. And they will still be dying — the 4,416th U.S. soldier to die in Iraq was killed in a Basra rocket attack earlier this week.

In an attempt to end what he once termed “a dumb war,” Obama ordered all but 50,000 troops to leave Iraq by Aug. 31. Those left behind will no longer be allowed to go on combat missions without being joined by Iraqi forces.

Much of that change was already put into effect last summer. A security agreement between Baghdad and Washington stopped U.S.-only patrols and raids in Iraqi cities, where most of the threat exists, after June 30, 2009. That same agreement requires all U.S. troops to be out of Iraq by the end of 2011.

“As far as boots on the ground, mainly it’s Iraqis doing the work,” said Gen. Ali Gadaun, commander of Iraq’s troop operations. “Of course, the Iraqis want to see this day coming, that their forces are in charge of the country and in charge of their security.”

In Massachusetts, where the president was on vacation, White House counterterrorism chief John Brennan called the drawdown in U.S. troops a “truly remarkable achievement.” He noted that the milestone had been reached a week ahead of schedule and represented a drop of 94,000 troops on Obama’s watch.

But Brennan acknowledged that the Iraqis still face sizable challenges, including forming a stable government and preventing terrorist bombings. “There’s still more progress that needs to be made inside of Iraq to ensure that security is going to prevail throughout the country and is going to be enduring,” he said.

Over 20,000 American soldiers in Iraq have been assigned to “advise and assist brigades” and will continue patrols and training exercises with Iraqis. Fewer than 5,000 are special forces who will team up with Iraqi troops on counterterror raids and other high-risk missions.

The rest of the 50,000 — about half of the U.S. force in Iraq — are high-ranking officers and headquarters staff who mostly will be planning military strategy through the final withdrawal.

Gen. Ray Odierno, commander of U.S. forces in Iraq, leaves Sept. 1 after more than five years there.

“There is still danger. There are still going to be people who attack our forces. We all know that,” Odierno said Tuesday. Odierno said he worries that Congress next month will cut funding requests — from about $2 billion to $1 billion — intended to help Iraq secure itself from foreign threats.