A veritable traffic jam clogged the British army checkpoint into Basra today, five lanes of disorder squeezed into one.

Battered orange-and-white taxicabs jostled with four-wheel drive vehicles piled high with plastic crates filled with fresh tomatoes, onions and potatoes. Crowded minivans competed for space with flatbed trucks, a motorcycle and even a bicycle, while men in black robes and red-and-white kaffiyehs stood on the roadside talking somberly and trading gossip.

The scene was almost normal, an ordinary market day, except for the British soldiers searching vehicles entering Basra and subjecting pedestrians to kaffiyeh-to-sandal pat-down searches. People were leaving Basra, too, making for a near-continuous two-way flow: families with small children, buses filled with passengers, vans, four-wheel drive cars, and the occasional ancient taxi sputtering past British Warrior armored vehicles and massive, 100-ton Challenger II tanks.

For more than 10 days now, Basra has been in a strange state of siege. British troops on the edge of the city and Iraqi soldiers and paramilitary units inside have been locked in a stalemate, playing what one soldier described as a deadly game of cat-and-mouse that changes dramatically after sundown.

At night, Iraqi tanks move from the center of town to the very edge of the city, just on the other side of this bridge. Iraqi fighters armed with assault rifles and rocket-propelled grenades fire on the British positions.

The British fire back with artillery -- when they can see their targets -- and sometimes chase after the tanks with their own armored vehicles until the Iraqis reverse gear and retreat back into the city's dense streets. "They reverse back and just sit," said a British tank crewman. "They want us drawn into the street-to-street fighting. But we won't be drawn in."

The crewman, a sergeant, said his men on occasion have advanced from their position to about two blocks into the city, only to return. "It's just the outskirts of the residential area," he said. "That's the furthest we've been into Basra."

Two nights ago, he said, his men were called in to try to find and destroy a dozen Iraqi tanks that had moved to the edge of town, taunting the British with their presence. By the time the British armor arrived, all but one of the Iraqi tanks had pulled back -- and the one left was destroyed.

When they are able to identify an Iraqi position firing mortars, the British troops launch their own artillery strikes. Sometimes, U.S. air controllers based at Basra International Airport call in air assaults by U.S. war planes and helicopters. The tit-for-tat attacks usually begin at dusk and continue until dawn. Thundering booms shake the earth and are occasionally punctuated by bright flares.

But by day, the constant movement of people back and forth across this bridge at the southern entrance to Basra carries an unreal air, as if the war were a remote concern compared to the rhythms of everyday life -- people needing to shop, to travel, to visit friends and relatives.

The residents of Basra have been described by the U.S. military as "human shields," being held in the city against their will by members of the Iraqi military and militia. But the soldiers here say that most of those leaving the city appear to be going out just for the day to the markets in Zubair, a town about 10 miles southwest of here, and returning voluntarily.

"They're not coming out to stay," said a soldier guarding the bridge. "They're not leaving with their household goods. A lot of them are going out to get tomatoes. It's not a great outflow of refugees."

Some reports from U.S. and British officials said Basra residents who did leave had family members held back as hostages to ensure their return. But the soldiers, and reporters who stood with them on the bridge, saw entire families leaving together -- men, women, children and infants -- and the flow was in both directions.

"A lot are coming in and out with their families," said a British major who spent the day posted at the bridge. "There's been a reasonable stream of traffic."

Soldiers at the checkpoints said they had caught some Iraqi fighters, members of the regular army, trying to leave the city by mixing in with civilians. Some were spotted wearing military boots, others were caught because they had their uniforms rolled up in plastic bags. They were taken to a nearby camp for prisoners of war.

What seems surprising about the standoff is that after 10 days of often heavy artillery and air bombardment -- including at least two strikes on offices of the ruling Baath Party -- Iraqi fighters holding out inside the city appear to be as tenacious as ever. And although the Iraqis have doubtless lost some armor and weaponry to the consistent artillery barrages, they still hold enough armor and mortars to keep British troops at bay and harass them nightly with mortars and rocket-propelled grenades.

British officers insist that the defenders' hold over the city has been seriously degraded over the last 10 days. "The army has basically withdrawn," said a British officer on duty here. "Now what's left is the militia."

"We know from different sources that the Baath Party in Basra is at the point of collapse," he said. "But we can't go in there with all guns blazing. We want to keep the civilian casualties to a minimum."

Some British soldiers expressed frustration that militia tactics have stymied their plans to move in and secure Basra and that a battle that was supposed to last for days has instead dragged on into its second week.

"We do raids and things," said a soldier. "But we don't have a foothold in Basra yet. It's taken longer than we thought. We were supposed to be in Basra two weeks ago."

"We don't have any foothold there. We haven't left any men there," said the British sergeant, who was involved in the incursion two blocks into the city. He added, "We're just sitting around waiting."

A British soldier watches Iraqis leave Basra through a checkpoint south of the city. Many appeared to be going to markets in a nearby town. "It's not a great outflow of refugees," one soldier said.Members of a British unit enter the Baath Party headquarters in an Iraqi village near Basra looking for party members. They did not find any.