WASHINGTON -- On the road to Baghdad, after suspiciously eyeing some Iraqis standing next to a pickup truck, battalion commander Philip DeCamp talked to his men about telling good guys and bad guys apart.
"It's hard, isn't it?" the lieutenant colonel asked. "Figuring out who's friendly, who's not. Who's a Bedouin, who's not. Who to hose. Who not."
It will get harder still if DeCamp, from the 4th Battalion of the 64th Armored Regiment, takes his soldiers into Baghdad in the days ahead.
Separating the enemy from innocents is just one of the perilous challenges if U.S. troops are thrust into full-scale urban warfare.
Unless Iraq capitulates before the fall of the capital, the city's rooftops, modern boulevards, sprawling neighborhoods and narrow, twisty side streets will test the coalition armies that are inching closer by the hour.
Military theory holds that an army unit loses almost one-third of its people taking a city - a price the United States hasn't paid for generations and hopes to avoid with new tactics and training, plenty of caution and a dose of luck.
Already, allied forces have engaged "rag tags in flip-flops," as British Sgt. Nigel Barton described poorly trained but dangerously unpredictable urban irregulars who might extend a hand of friendship one minute and shoot the next.
U.S. and British troops have struggled for four days to make secure their early conquest of Umm Qasr, the strategic port town where the Iraqi resistance has refused to melt from the streets.
Farther up the highway, allies closed in quickly on Basra, a city of 1.3 million, taking the airfield on the outskirts and a bridge. But there the assault paused, turning into a shooting match that persists.
Allies hope the Iraqis will give up before troops have to be sent into the city. "We're not going to get drawn in unless we absolutely have to," said British Col. Chris Vernon.
Basra is a smaller version of Baghdad, city of 5 million, home to Saddam Hussein's toughest defenders and the key to victory.
Allies face a multitude of hazards if they have to mix it up inside "Fortress Baghdad," as Defense Secretary Donald H. Rumsfeld puts it. Military analysts say the worst case - actual door-to-door combat, with civilians always in the way - might be avoidable, but incursions of some sort into hostile urban areas are likely.
Beyond the obvious risk to troops moving through unfamiliar neighborhoods, the prospect of high civilian casualties gives leaders pause. After the 17-hour urban gun battle in Mogadishu, Somalia, in 1993, 18 U.S. servicemen and more than 1,000 Somalis lay dead - and not all the Somalis were combatants.
On the approach to Baghdad, the Army's 3rd Infantry Division has run into al-Quds militiamen who used a commercial area to stage guerrilla attacks. When U.S. tanks pursued, they quickly found themselves in a residential neighborhood, with women and children coming out of their houses to gawk at the Americans.
"The al-Quds are all along this area, dressed like civilians and driving civilian vehicles and they come out at night," DeCamp said Monday. "The al-Quds are madmen, taking over people's houses and making them get out."
For all that, some U.S. strategists say Fortress Baghdad can be taken, and not necessarily at tremendous cost.
"I don't think it's going to be a Stalingrad," said retired Marine Col. Bob Work, referring to the Russian city where 1 million died in a crucial defeat for German invaders in World War II.
He said the positioning of Saddam's toughest divisions outside the city raises hope they can be decimated by air attack rather than have to be pursued into urban warrens in great numbers.
He is clinging to that hope.
"In the city, everything is a line-of-sight fight," Work said. "You peek your head around the corner and you can see down one block. Enemies can pop out above you, below you. They can come from the sewers.
"They can shoot down on you from windows. They can outflank you by going down alleyways on the other side of the building."
Daniel Goure, a military analyst at the Lexington Institute, said allies would have to divide the city into manageable chunks, isolating the resistance.
"It will be a pain, it will be difficult, it will be urban," Goure said. "But it will work."
John Pike, defense analyst at Globalsecurity.org, predicted a three-pronged urban strategy - bombing leadership targets, sending in the tanks and seizing airwaves to urge surrender.
"Those three things simultaneously will hopefully convince people that Iraq is under new management," Pike said. "And if that doesn't work, then there's going to be a problem."
One way to fight in a city
This urban warfare tactic has been rehearsed by U.S. soldiers for the Iraq war, using the Bradley fighting vehicle:
-The Bradley reaches speeds of up to 45 mph, and carries infantrymen into battle, letting them out just a few dozen yards from the enemy.
-Four Bradleys make up a platoon, each carrying six soldiers that make up a squad. A platoon's vehicles arrive together at an objective and two squads get out and take cover behind the other two armored vehicles.
-The first two Bradleys stand back with their 25 mm cannons loaded with depleted uranium shells capable of piercing armor. The Bradleys also have a belt-fed heavy machine gun to use against enemy troops and two anti-tank missiles.
-The second two Bradleys approach the targeted building slowly, with the first two squads running alongside, keeping their eyes open for enemy troops. Once in position, the hatches on the last two Bradleys drop down and an additional 12 men run out; the platoon is ready to enter a building or walk down a narrow road where tracked vehicles can't move.
-Each infantryman carries a variety of weapons - a shotgun, an M-16A4 assault rifle or the new M-4 - either of which can be fitted with an M-203 grenade launcher - or an M-249 squad automatic weapon.
The assault rifles and the machine gun have laser pointers that are visible only through the night vision equipment worn by soldiers, allowing them to see exactly where they will hit the target.
-The Bradley uses a thermal imaging system to hit targets up to 3,000 yards away.
Associated Press writer Chris Tomlinson with the 3rd Infantry Division contributed to this story.
On the Net:
Marine Corps Warfighting Laboratory: http://www.mcwl.quantico.usmc.mil/