NEAR NAJAF, Iraq - Driving night and day, more than 70 American tanks and 60 armored troop carriers raced 700 miles across rough desert terrain - a bold flanking movement that placed U.S. forces less than a day's march from Baghdad on Sunday. 

The 3rd Infantry division, 2nd Brigade - also known as the Spartans - covered 228 miles in less than 40 hours to take up fighting positions ahead of all U.S. forces, about 100 miles from the Iraqi capital. 

Late Saturday, the brigade encountered dozens of Iraqi vehicles mounted with machine guns and fought until dawn Sunday, destroying 15 vehicles, killing at least 100 Iraqi militiamen and capturing 20 prisoners of war. 

The Iraqi fighters were believed to be members of the ruling Baath party militia, loyal to one of Saddam's sons. 

In this determined off-road march, the brigade's fighting vehicles covered more distance than the entire 100 hours of ground fighting in the 1991 Gulf War. 

Before the operation began, Lt. Col. Eric Wesley, the executive officer of the 2nd Brigade, said it would have taken six months to cover the same territory during World War II. 

The commander of the 2nd Brigade, Col. David Perkins, compared the march to another massive military undertaking - that of a Carthaginian general who surprised the Romans in 218 B.C. 

"I'm using the analogy of Hannibal taking elephants over the Alps," Perkins said. "But instead of the Alps, there are big waddies (gulches) out there and the elephants are the tanks." 

Perkins split the brigade in two parts; the first, nicknamed "Team Heavy Metal," included the armored fighting vehicles, while the second, dubbed "Rock 'n Roll," consisted of all the wheeled support vehicles. 

The combat vehicles wove cross-country through the remote desert, avoiding cities, villages, main roads and highways to keep Iraqi forces from detecting them. They traversed the sand in wide wedges, sometimes up to six miles across, speeding at 40 mph and leaving huge plumes in their wake. 

The only people they encountered were Bedouin tribesmen, herding sheep, goats and camels, who stopped and stared as the armored wave passed. 

Inside the Bradley fighting vehicles, six infantrymen sat closely together, their chemical protection gear soaked in sweat as they bounced across the desert for five hours at a stretch. The brigade stopped only to refuel. 

Perkins has said the goal of the operation was to send a message to Saddam about how fast the U.S. military can move and how useless it would be to fight. 

"There is a psychological component. If the president (Bush) can say, 'Look at your window, there is a tank brigade outside,' that can hasten the fall of the regime," he said. 

Advance Kiowa observation helicopters and long range ground patrols watched the road ahead for the massive convoy. 

As night fell Saturday, suspected Baath party militiamen began chasing the patrols, causing the brigade to stop about 20 miles short of its destination. While one unit provided supporting fire, another regiment advanced to face the Iraqi troops. 

"We've got a ... firefight, OK Corral out here," said Lt. Col. Philip DeCamp, describing the situation to his company commanders. 

The battalion moved forward and captured ground near the city of Najaf with little resistance early Sunday. Najaf is on the western bank of the Euphrates River, along one of the main highways leading to Baghdad. 

Mosques in Najaf and Karbala are the most sacred sites to Iran's majority Shiite Muslims, after those in Saudi Arabia. 

Najaf is the site of the tomb of Imam Ali, the son-in-law and cousin of Islam's Prophet Muhammad. Shiites aspire to bury their dead in its cemetery, which stretches for miles and is the largest in the Muslim world. 

Also Sunday, coalition troops were battling Iraqi forces in Umm Qasr, a stratetic port city in southern Iraq. Its modern docks complex, adorned with huge portraits of Saddam, was secured Saturday, according to the U.S. Central Command, but coalition forces on Sunday were still trying to rout "pockets of resistance," said Capt. Al Lockwood, spokesman for British forces. 

"In some areas the forces give up easily, or retreat, or surrender, and in other places diehards - people that want to fight to the death - carry on fighting," British spokesman Lt. Col. Ronnie McCourt said. 

"Just because you've been through an area once, doesn't mean to say that you've complete confidence that it won't spring up again." 

Umm Qasr, Iraq's only deepwater port, is strategically vital as a conduit for shipments of humanitarian aid to the war-torn nation. 

Some of the Iraqi forces had changed into civilian clothes to blend in with the residents. Iraqi officials in Baghdad called the resistance in Umm Qasr "heroic," and said images of the fighting, broadcast around the world, proved the coalition was not in control of the city. 

In addition, coalition forces were "on the outskirts of Basra," the second-largest city in Iraq, but haven't yet secured it, Lockwood said. 

Shelling could be heard from Basra on Sunday, and thousands of Marines were trekking north toward the city along Highway 80, which was known as the "highway of death" during the 1991 Gulf War. 

Iraqi officials said allied airstrikes on Saturday killed 77 civilians in Basra and injured more than 500 other Iraqis in four cities.