Banditry and lawlessness appear to be spreading through some areas in southwestern Iraq as British troops sweep the countryside for remnants of Iraqi forces and remain at a stalemate with fighters in Basra, Iraq's second-largest city.

Villagers in this area now complain of roving bands of armed men who steal tractors, hijack trucks, loot factories and terrorize residents with near impunity.

At the same time, Iraqi paramilitary fighters inside Basra fired mortars and machine guns today on about 1,000 civilians trying to leave the besieged city, forcing them to retreat, British military officials said. According to British pool reporters accompanying the military, Iraqi forces used mortars mounted on pickup trucks to fire on the civilians. A spokesman for the British forces in the Persian Gulf region, Lt. Cmdr. Emma Thomas, said an initial group of about 1,000 people made it out of the city safely, fleeing to the west of Basra, but the firing started when a second group of the same size tried to leave.

Last week, after U.S. forces swept through southern Iraq in their rapid push toward Baghdad, they left behind a vacuum of power and authority that British troops stationed here say they are reluctant to fill.

"This is getting to be peacekeeping duty, like in Bosnia and Kosovo," said one British Fusilier, a member of the famed Desert Rats. "I came here to fight a war."

A member of a Challenger II tank crew recalled that on his first day in the village of Mushirij, six miles west of Basra, he was called upon to help track down someone who had stolen a villager's tractor. "I had to chase it down with this thing," he said, pointing to the 100-ton British tank. "The tractor was going about 10 miles an hour."

Villagers in Mushirij gathered today outside the command post of the Fusiliers' Zulu Company, complaining loudly that while the U.S.-led invasion of Iraq, dubbed "Operation Iraqi Freedom," promised them a better life, after just one week they have seen only heightened insecurity.

The main problem, many complained, is that while the British troops patrolling here confiscate weapons from ordinary villagers, the thieves -- many of them deserters from President Saddam Hussein's 51st Mechanized Division that was based here -- roam outside the control of any authority, preying on villagers.

"The Americans occupied us. They said they would protect us," said a 47-year-old Iraqi man, an engineer in bluejeans and black sandals with a moustache streaked with gray. "But the thieves come and steal from our companies. How can we restart our companies?"

"We are afraid from both sides," said the man, who asked that his name not be published. "We are afraid of the thieves, and we are afraid of them," he said, pointing at the British troops garrisoned in what was the headquarters of the ruling Baath Party. "The thieves have guns, but we have no guns."

He added, ominously, "If this continues, in seven days or more, we will fight them," he said, referring to the British soldiers. "We have no guns, but we can get guns. If this place is still without water, still without electricity, we will fight them. Even this child," he said, patting the head of an 8-year-old who was listening intently in the crowd.

"He can fight," the engineer said of the child. "He is an Iraqi."

Most of the people in this area work for one of the four complexes that belong to the Iraqi state oil company. The largest one, the refinery, employs about 3,500 people, although there has been no work here since the start of the war. Now, the abandoned facilities have become a favorite target of the bandits.

"They stole from our company -- air conditioners, machines, cars, trucks," said another middle-aged man, also an engineer with the company. "And this force here doesn't protect."

Before last week, he said, security was not a problem. "There were police, and they had stations around this area." But now, he said, "There are no Iraqi police. And no one can carry a pistol -- it is a crime now."

At one of the smaller facilities of the oil company, workers today were using a bulldozer to build a dirt wall around the entrance. "We are closing this, so the thieves won't come," said Kadim Kassim, 59, an employee of the oil company for some 26 years. "There's no policeman, no watchman. No anything."

He said the village did not lack food or medicine, only fresh drinking water, since the supply was cut at the outset of the war. The main issue, he said, is security. "We need police," he said. "We want police to save this place."

The British troops apprehended some thieves when alerted by the villagers. On a drive down a gutted and muddy path, reporters saw British soldiers forcing several Iraqi men out of a truck. The men were made to stand with their hands against a wall while they were frisked.

Just after noon in Mushirij, British troops marched four other suspected thieves through the crowd to the Zulu Company headquarters, where the villagers outside jeered them and shouted, "Ali Baba! Ali Baba!" in a reference to the character from the "Thousand and One Nights". The suspects were young men with light beards whose heads were wrapped in red-and-yellow checked keffiyehs. Three minutes after they were brought in, they walked out the gates, free, smiling.

British commanders say there is little they can do. To punish the thieves, "We give them a ticking off, in a very robust British manner," said Maj. Duncan McSporran, who concedes that he has become something of a town sheriff. "I am the sheriff, aren't I?" he said. "That's one of my many functions."

But with troops still engaged in a military operation, disarming the population, searching for weapons caches and continually fighting low-level guerrilla-style attackers, he said, the soldiers have their hands full without the added burden of policing street crimes. "We don't have the manpower. We don't have the resources," McSporran said.

The initial plan, at the start of the war, was for British military police to move into southern Iraq quickly and begin building a new Iraqi police force. "Our job is to work with the local police -- not to change all their practices, just to make sure they're not killing people. The plan is to get rid of the hierarchy and to work with the others," said a British military policeman.

But that plan has been made more difficult by guerrilla attacks. The British say they are not budging on their "no weapons" policy and will continue disarming the population. "They don't need them," McSporran said. "I've told them, if they believe there are thieves, come and tell me."

A family flees the southern Iraqi city of Basra, where Iraqi forces fired mortars and machine guns at civilians trying to leave.