On Wednesday morning alone, diggers unearthed two large and intact urns, a delicate vase, the leg to a statue of what might have been a bull or a calf and countless small engraved artifacts.

On the outskirts of the site, people furtively offered to sell sculptures and ancient cuneiform tablets. A man in his 40's displayed what resembled a large oval ornament that was entirely covered in lines of cuneiform writing.

''Five thousand dollars,'' he demanded.

The looting is not limited to here, the archaeologists say. Iraq, which occupies what was ancient Mesopotamia, has more than 10,000 registered archaeological sites. But experts say the real threat is to 15 to 20 major sites atop ancient cities like Larsa, Fara and the great Sumerian city of Erech.

''We believe that every major site in southern Iraq is in danger,'' said Donny George, director of research at Iraq's State Board of Antiquities and Heritage, which oversees all archaeological excavations in Iraq.

''We used to have guards there,'' he added. ''But now they are either pushed away by the looters or they are working with thieves themselves in one way or another.''

The looting here, and at other locations, is another result of the anarchy and lawlessness that continues to plague Iraq six weeks after the collapse of Saddam Hussein's government.

President Bush's new civilian administrator for Iraq, L. Paul Bremer III, has moved aggressively to rein in looters in Baghdad, and the American armed forces have greatly expanded street patrols by military police.

But with a few exceptions, the American forces have done little to protect Iraq's numerous archaeological sites, just as they stood by while Iraq's museums were looted in the days after the Hussein government fell. Army and Marine units occupy several bases within 30 miles of here, but so far they have done little to stop the treasure hunters who first began swarming around here two weeks ago.

Residents in the nearby village of Afak said today that an Army helicopter had landed at Isin on Wednesday afternoon and shooed off looters with warning shots in the air. Military officials at three bases in the city of Diwaniya would neither confirm nor deny the villagers' reports.

The present looting is reminiscent of widespread episodes of plundering at Iraq's thousands of archaeological sites that continued for years after the 1991 Persian Gulf war. What began then as isolated crimes by individuals soon developed into organized hunts involving throngs of people, similar to what can be seen here today. Those raids often were said to be organized by outside gangs from neighboring countries that would fence the artifacts to Western art markets, where artworks and relics from unguarded sites greatly surpassed that stolen from museums and other institutions.

It was not immediately clear whether the looting going on now has reached that level of organization, or how the stolen artifacts were being disposed of.

Material from Iraq, which archaeologists said was fairly limited before the 1991 war, grew so prevalent that cuneiform tablets are even now regularly advertised on e-bay, and can sell for less than $100.

Beyond the loss of potentially priceless artifacts, archaeologists say, looting such as that underway in Isan Bakhriat all but destroys the ability of researchers to assemble a mosaic of meaning from the shards of old art and sun-dried bricks.

Where archaeological teams spend years and even decades cataloging sites, excavating with small knives and brushes, the looters have been overturning tons of dirt daily.

Ms. Osthoff, who returned to Iraq shortly before American forces overthrew the government of Mr. Hussein, was alerted by local villagers who were horrified by the destruction at Isin.

Protected by old friends, Ms. Osthoff waded into the mob of heavily-armed diggers four days ago and then escorted two journalists to the site again on Wednesday.

''They are poor people, and they are desperate to make some money,'' she said today. ''But they do not understand what they are doing.''

Armed with shovels, picks, knives and AK-47's, men ranging from teenagers to middle age have transformed the once-manicured archaeological site into what looks like a scene from the movie ''Holes.''

The men arrive shortly after dawn, sometimes by motorcycle and truck but often on foot -- a three-hour walk from the nearest village.

A man who served for years as an armed guard at the site, and who would give only his first name, Jassim, still stands by with a loaded Kalashnikov. But he does not try to stop or even discourage the intruders, and often peers enthusiastically at their latest discoveries.

''What can I do?'' Jassim said. ''I alone cannot stop the whole village. Even if I try to arrest them, what do I do after that?''

Despite the allure of easy money, some villagers have been shocked by the looting at sites where they themselves worked for years and learned the painstaking methods of mapping a site inch by inch.

''Every person who puts his hands on these things is bad,'' said Abdulsadiq al-Abed, a 68-year-old Bedouin who worked with German and French excavation groups for 25 years. It was one of Mr. Abed's sons who drove to Baghdad last week to seek help from Ms. Osthoff.

A small and wiry man who moves slowly these days, he looked brokenhearted and ashamed at the plundering underway. ''If I tell them not to do that, they will shoot me,'' he said. ''We have no government to watch them and no police to stop them.''

Isin's relative remoteness in the desert makes it more difficult to protect than other sites, and its rich payload of artwork and ancient tablets make it an irresistable lure.

Some of the diggers seem barely aware that what they are doing is illegal. At one pit on Wednesday, a man in his early 20's eagerly motioned to foreign visitors to come see his newest find.

Nothing seemed visible at first. But then the young man reached his hand into the wall of the pit and withdrew what appeared to be the femur of either a man or an animal.

Ms. Osthoff, rushing over, gently doused the object in water and wiped off some of the mud.

''You can see here that this is the leg of an animal and this is the hoof,'' she said, pointing to a black ring at the base and to remnants of reddish-brown coloring above it that gave the appearance of fur.

''But look here,'' she added. pointing to areas along the leg that had been freshly sheered away. ''They have ruined it with the cuts they made.''

Such details seemed to matter little in the frenzy of the treasure hunt, but to archaeologists, as opposed to art collectors, they speak to the heart of the problem.

''If you find an artifact but you don't have the context, you lose 80 to 90 percent of the information,'' said Dr. George of the Iraqi State Board of Antiquities. ''Every single hour, every single day this goes is a great loss of information.''

Copyright 2008 The New York Times Company

by CINDY HO