The wreckage still smoldered long afterward, burned-out tanks and charred troop carriers strewn along a Baghdad highway, overturned antiaircraft guns and the twisted carcass of a motorcycle before the landmark Um Taboul mosque. Tank treads plowed across street medians, and a lamppost lay mangled across an incinerated pickup.

In front of Yarmouk Hospital sat an orange-and-white taxi, its windows shattered and blood smeared across the driver's door.

The entry of American forces into the capital today woke residents with a display of brief but devastating power that signaled the climax of the U.S. march across Iraq and the beginning of the battle for Baghdad.

Within hours, the city took on the guise of war. Republican Guard troops, wearing the distinctive red triangle insignia, seized homes along the front line, and Iraqi tanks, armor and artillery poured into the capital. For the first time since the war began, the black-clad militiamen of Saddam's Fedayeen carried rocket-propelled grenades in the streets. Thousands of residents fled for the tranquillity -- what little there is -- to the north and west of the capital.

"Nobody knows how long this will last, except President Bush and Saddam Hussein," said a 33-year-old resident of the Bayaa neighborhood.

He and other residents said they awoke at 6:30 a.m. to a pitched battle less than a mile from their homes. Machine-gun fire broke the silence, followed by a cascade of grenades and tank fire.

"The tanks are close, the tanks are close!" one resident said his young daughter yelled.

Another resident said they saw droves of Baath Party militiamen, clad in green and carrying rifles, rushing toward a street where the American forces methodically advanced. In confused scenes, others said, they saw Iraqi soldiers running away from the battle. Families hid in hallways, away from windows and doors.

The incursion seemed more symbolic than strategic, a message that U.S. forces could move at will into the seat of Hussein's power.

Crossing three outlying neighborhoods, M1 Abrams tanks and M2 Bradley Fighting Vehicles moved rapidly and without any apparent fixed objective. But the destruction in their wake was formidable: the charred remains of at least 16 pickups, cars, trucks and personnel carriers, some with Republican Guard insignia; six antiaircraft guns overturned or still burning near the Dora grain silo; damage to a bridge on the road to Saddam International Airport; the wreckage of at least two tanks. It was not known how many casualties resulted.

By 9:30 a.m., it was over, and the government deployed in force.

For weeks, Baghdad was remarkable in its lack of a military posture. The only sign of the ground war in southern Iraq were the knots of Baath Party militiamen who had taken up posts across the city. Their numbers dramatically multiplied today, outnumbering residents in the streets in much of Baghdad. Along with police, they manned checkpoints on the edge of a city that more and more looked deserted.

Saddam's Fedayeen gathered, most in their distinctive black uniforms, but a few choosing a more personal touch -- white gowns, red-and-white kaffiyehs or a white turban. They intermingled with groups of soldiers underneath the canopy of palm trees, some lugging mortars, antiaircraft guns, heavy machine guns, rocket-propelled grenades and rifles.

Joining their ranks were males in civilian clothes carrying guns, some appearing to be in their mid-teens. In one square, men with the Fedaan tribe raised their red flag over a sandbagged position, suggesting the government had called on tribes from the countryside to aid the city's defense. Trucks carrying water and fuel shuttled between positions throughout the day.

By nightfall, there were signs the government would concentrate its forces closer to the city's center. Soldiers dug trenches along roads that enter Baghdad from the south. Tanks were parked at major downtown intersections like Nisoor Square. Under a bridge near the Baghdad Central Railway Station, soldiers erected chest-high dirt barriers, with police and Baath Party militiamen directing traffic to alternative routes.

"It's a historic time," said Raed Saeed, a 34-year-old electrical engineer in Karrada, an upscale neighborhood cut off from the rest of the city by a bend in the Tigris River. "What is happening is something we will not forget for many years."

Like so many residents, either too afraid or too uncertain, he hesitated to say what that something was. "All things are mysterious, all things are mysterious," he said. "I can't expect what will happen tomorrow or after tomorrow."

As with so many days recently in Baghdad, today blended scenes of desperation with elements of the bizarre. Iraqi officials declared that victory was as near as ever. They denied U.S. troops had entered Baghdad and claimed they had retaken the airport. In battles there, they said, 200 U.S. soldiers were killed.

"We are surrounding them and pounding them," Information Minister Mohammed Saeed Sahhaf declared at a daily news conference. "The whole trend has changed and we are going to finalize this very soon."

Sahhaf read another statement from Hussein, who was shown on Iraqi television on Friday touring the city for the first time since the 1991 Persian Gulf War, holding a baby and slapping the hands of Baath Party militiamen, some of whom kissed his hand.

"You must inflict more wounds on this enemy and fight it and deprive it of the victories it has achieved," the statement said. "You must rattle their joints and terrify them and speedily defeat them in and around Baghdad."

As fighting raged on the city's outskirts, the government managed to organize a noisy parade of police cars careering through downtown, their sirens blaring. They fired rifles in the air as they passed the Palestine Meridien Hotel, where most journalists are staying. But the streets they drove were deserted.

Across Baghdad, isolation was a growing theme. A blackout has deprived parts of the capital of water and electricity, and bombing has destroyed the telephone network. Furtively, residents passed messages to the few in Baghdad with satellite phones to contact relatives abroad, if only to say everyone was safe. Others made harrowing drives across a city jolted by bombing to make sure loved ones were out of harm's way.

At Yarmouk Hospital, 22-year-old Ahmed Jassim barged into the nurses' station. Sweating and impatient, he gazed at a pink piece of paper. On it were the names of the injured admitted -- Omar Bahaeddin, Ali Hasan, Abdel Qadir Adil and so on. He shook his head and tried to get the attention of a nurse, overwhelmed with the task of managing rooms full of wounded.

"I'm looking for my brother," he pleaded. "We can't find him."

The nurse checked the list again for the name of his brother, 26-year-old Hamad Jassim, who ran a vegetable stand on Baghdad's outskirts. She couldn't find him either. Perhaps at another hospital, she said. He turned abruptly and ran down the hall toward the exit.

Others joined tens of thousands of residents leaving the city, some paying taxi fares that had increased 16-fold over the past few days. The signs of their departure were everywhere. Lines snaked around gas stations, longer than at any time since the anxious eve of the war. Whole blocks on the city's southern outskirts were deserted, some houses abandoned and others seized by the army and Republican Guard troops preparing for street-to-street battles.

Mustafa Kamel drove all night to take his family of 27 to the village of Hit, about 100 miles northwest of Baghdad along the Euphrates River. The trip should have taken a few hours, but the highway, he said, was packed with families fleeing the capital. Of the eight families on his block, only two remained, and one of them might leave soon.

"The way is paralyzed from here to Hit," he said.

The war, he predicted, would last days, perhaps much longer. Deep down, he said, he believed Hussein would somehow manage to survive, as the president has managed to dominate so many aspects of life here, lurking in every conversation, every whisper.

"I swear to God, he will remain," Kamel said.

But he wouldn't stay to find out how. He planned to finish packing his bags, shutter his business and then join his family Sunday, leaving a house that was frozen in time -- tea cups half-empty and ashtrays flowing over with cigarette butts. Sofas were pushed against doors, a half-hearted attempt to deter looters. But with war at his doorstep, he no longer cared to be a spectator.

"It's a movie and we don't know the end of it," he said.

Baghdad residents investigate the wreckage of an armored personnel carrier destroyed during a brief, fierce battle.