As Army troops barreled into the heart of Baghdad today, a unit from the 2nd Brigade of the 3rd Infantry Division was ordered to hold onto a key cloverleaf in the southern part of the city, a mission that sounded routine but quickly turned into five hours of killing and fiery chaos.

An Iraqi rocket-propelled grenade slammed into a U.S. ammunition truck at the intersection. As mortar shells aboard the ammunition truck exploded, they set a nearby fuel tank truck ablaze, sending clouds of black smoke billowing into the sky. With the cloverleaf now an inferno, soldiers dived for cover or ran for their vehicles. Two Special Forces vehicles -- Toyota pickup trucks -- went up in flames.

"RPG on the roof! RPG on the roof!" yelled one soldier from beneath an overpass as he peered through binoculars at a building ahead. M2 Bradley Fighting Vehicles and other armored vehicles poured 25mm cannon and machine-gun fire at the target, but the incoming rounds continued.

"Get out of here now!" a sergeant bellowed.

At least two soldiers of the 3rd Battalion, 15th Infantry Regiment task force were killed and four were wounded in the battles, which were fought without air support. Commanders said air missions were called off because of antiaircraft fire and the thick ocher haze that hung over the city. U.S. jets bombed targets in Baghdad later in the day, however.

Two of the wounded U.S. soldiers were victims of friendly fire when an artillery round from a Paladin 155mm self-propelled howitzer fell far short of its intended target -- the building where Iraqi snipers and militiamen were spotted firing rocket-propelled grenades. Instead, the round landed on the stone embankment of one of the cloverleaf ramps, about 50 yards from troops holding the intersection.

First Sgt. Chris French estimated that at least 25 Iraqis were killed in the fighting, and about 30 others threw up their hands and surrendered when infantrymen of the 3rd Battalion's Bravo Company cleared a series of trenches and bunkers in and around the intersection. The surrendering loyalists, members of Saddam's Fedayeen and other militia groups, were ordered to strip when they emerged from the trenches as a precaution against suicide attacks.

"Do not wave them to you!" Capt. Ronny Johnson, the Bravo Company commander, yelled at his platoon leaders as the first group of fighters came forward. "Make 'em strip! I want these guys butt-ass naked!"

Some of the captured loyalists were forced to remove all their clothing, but most were allowed to keep their underwear on. Several had been wounded before giving up.

One of the prisoners said he was Syrian, part of a group of 5,000 from his country that he said volunteered to defend Iraq, according to French. Hundreds of rocket-propelled grenade rounds were found in the trenches with the loyalists, he said.

An Army medic, Sgt. Mario Manzano of St. Petersburg, Fla., said one wounded prisoner offered him a thick wad of Iraqi dinars for treating him. When he refused, Manzano said, the Iraqi man began weeping, thanked him for the medical treatment and denounced President Saddam Hussein in broken English.

After setting out from the junction of Highway 1 and Highway 8 south of the city this morning, the Bravo Company convoy drove past dozens of burned-out Iraqi vehicles and charred bodies on the way to downtown Baghdad and the cloverleaf it was assigned to secure. Three ammunition trucks, turned into smoking hulks by direct hits, lay in the highway's southbound lane, their cargoes of artillery and mortar shells strewn on the asphalt. One wrecked truck was pulling a trailer containing a mortar tube.

Civilian passenger cars and trucks were also among the blasted vehicles, some with corpses inside. One blackened body lay beside the wreckage of a motorcycle. Whether they were fighters heading south to engage the Americans or luckless civilians trying to escape the city remained unknown.

In one lane lay dozens of land mines, each secured onto the asphalt by a little mound of dirt.

Shortly before 10 a.m., word came over the company radio that Hussein had ordered all militants to join their units for "one last stand."

"You'll be moving into heavy contact," Johnson told his troops as the column drove past a huge portrait of Hussein at prayer.

Steadily, the convoy pushed past factories, military compounds and warehouses, all constructed of the same sand-colored brick and plaster. By the time the convoy reached the cloverleaf, the Bradleys, Humvees and support vehicles were under fire. The smell of cordite hung in the air. Muzzle flashes were spotted from buildings ahead.

"Be advised, the suicide bombers are out," Johnson told his troops on the radio.

"We've got enemies coming from the north!" shouted one platoon leader.

"Engage and destroy," Johnson ordered.

From then on, any vehicle that approached from the north was considered fair game. Several civilian vehicles were blasted with 25mm high-explosive rounds and machine-gun fire, their passengers assumed to be hostile.

Then came a radio report of enemy bunkers to the rear, south of the cloverleaf and even within it, a few dozen yards from the column's vehicles. Infantrymen poured out of their Bradleys and began moving down the trench line, occasionally firing into it. Fighters hiding in the trenches began to surrender, raising their hands and climbing out.

From its spot beneath an overpass, the nose of an M88 armored recovery vehicle occasionally ventured forward to poke out from the shadows. Staff Sgt. David Fields, the vehicle's commander, ordered his driver and mechanic to keep a sharp lookout. Through his binoculars, the mechanic, Pvt. Luke Tate, a 28-year-old farmer from Missouri, repeatedly picked out targets behind fighting positions on the ground or in the windows of tall buildings ahead, and Fields opened up on them with his M-16 rifle or the .50-caliber machine gun mounted on his turret.

"There's still someone in that left back window," Tate said after directing fire at men he said were holding rifles and RPGs.

Fields, 38, of Lee's Summit, Mo., picked up his M-16 and fired. "They were firing AKs at us, but they didn't get any RPG rounds off," Tate said, referring to AK-47 assault rifles.

That luck did not hold. As the morning stretched into afternoon and the company stayed put, enemy combatants filtered into the area, opening fire on the Americans in and around the cloverleaf. Then, shortly after 1 p.m., a column of resupply trucks, including fuel tankers, pulled up from the south.

"We've got the whole support platoon showing up," French said on the radio.

"Who the [expletive] brought these guys all the way up here?" Fields muttered. "What a bunch of idiots."

"I didn't ask for them to come up here," French added. "We really haven't consolidated yet."

Johnson radioed that the resupply was for two other battalions that had gone ahead and were running short of ammunition.

"I'm fully aware of [that], but this is not a good place to stop," French replied.

He was right; the fighting intensified. Inside the M88, hot brass shell casings poured into the open hatch, covering the vehicle's floor, as Fields blasted away with his 7.62mm machine gun.

"This bitch is almost over," said the driver, Pvt. Damon Winneshiek, a Native American and a former blackjack dealer in a Wisconsin casino. "These guys are going to have to give up soon."

"I just don't believe we're sitting here," Fields said.

As the fighting continued, five naked prisoners were escorted back to the cloverleaf from a trench that the infantrymen cleared in the northwestern corner of the intersection. Then the RPG round arced into the ammunition truck, and it was bedlam.

Fields and Tate poured fire into the building about 400 yards ahead of them, Fields shooting his machine gun and an AT4 antitank missile and Tate firing his M-4 automatic rifle.

"Load up all the dismounts, a section at a time!" Johnson ordered. It was time to leave.

The infantrymen piled into their Bradleys. Once everyone was accounted for, the convoy resumed its northward push, the armored vehicles protecting the fuelers and ammo trucks needed by the other battalions ahead.

All along the route, fighting continued, machine guns and Bradley cannons opening up on targets in front of the column and on both sides. At one point, an RPG round hit the side of a bridge just as the M88 was passing under it, missing the turret by several feet. Another RPG round struck the M113 armored personnel carrier of French, the company first sergeant. But it bounced off. A dud.

Arriving at Hussein's Sijood Palace, where they pulled up for the night, Fields ordered Winneshiek, the M88 driver, to knock down the wall and iron fence of a compound bordering it, using the 56-ton vehicle as a battering ram.

"You busted the palace wall," Fields told the quiet 25-year-old private afterward. "You can brag about that the rest of your life. You broke the palace wall."

Troops of the 3rd Infantry Division are entrenched near a bridge in northern Baghdad. Another unit in the division fought for control of a key intersection in the southern part of the city.Sgt. Christopher Ferguson of Task Force 2-69 Armor, 3rd Brigade Combat Team, 3rd Infantry Division, mans a .50-caliber machine gun during an advance in northern Baghdad.