hops and restaurants in the retail concourse beneath 5 World Trade Center were looted in the wake of last week's disaster, and police detectives are investigating whether rescue workers were responsible, law enforcement officials said yesterday.

The looting, which a New York National Guard infantry unit discovered, appears to have begun soon after the fires in the upper stories of the building were extinguished last week, and continued in a less aggressive fashion through Tuesday night or early Wednesday morning of this week, said Capt. Vincent J. Heintz, commander of Company C, First Battalion, 105th Light Infantry.

A warren of wide subterranean passageways in 5 World Trade Center, on the northeast corner of the plaza, somehow survived the collapses of the twin towers and the searing fires that raged in that building overhead throughout the day of Sept. 11. One level below ground, many retail stores and restaurants, as well as the subway stop there, are intact. Even the water damage was minimal.

Together the passageways and shops form an eerie Pompeii, a hushed and lightless world of ash, shards of glass and crumpled ceilings, interspersed with scenes of a New York City morning frozen in time. Several officers and soldiers who entered the basement said the thieves who swept through had acted as if they were raiding a tomb.

The looters picked through a Tourneau boutique watch store, raided cases of designer sunglasses in another shop, tried to pry open at least one cash register and penetrated the service room behind a row of Chase automated teller machines, where steel safes appear to have dissuaded them from making off with stacks of cash. Early this week the Guard reported the crimes to the police and Robert M. Morgenthau, the district attorney. Police investigators and union officials toured the concourse Wednesday night, and Daniel Castleman, chief of the district attorney's investigations division, said he spoke with police officials to express concern about security at the site.

On Sept. 13, two men � including a former city correction officer who was posing as a police officer � were arrested and charged with stealing two watches at the Tourneau shop, Mr. Castleman said.

He said yesterday that the looting in the past week appeared limited to a few shops under one building.

"It's not a situation of everyone walking in and stuffing their pockets," he said. "It could be one guy who was very determined, and got his hands on some merchandise. At this point we don't have evidence of who it was, when it was, or precisely what was taken, and the Police Department, understandably, has taken an interest in it."

Deputy Commissioner Thomas Antenen, a police spokesman, said the department was reviewing the facts of the case. "We arrested two looters last week, and have received these reports of other missing property," he said. "We are looking into it."

Guard officials have exercised painstaking care not to blame any particular group of rescuers, saying the thieves could have come from any number of agencies working under the rubble.

"They could have been police officers, they could have been firefighters, they could have been contractors or National Guardsmen," said Captain Heintz, who is also a rackets prosecutor in Mr. Morgenthau's office.

Guard officials noted that it was virtually impossible for civilians to reach the underground area, which is at the center of rings of security, immersed in darkness and cluttered at many points with hanging or leaning rubble.

They said they had little doubt that the thefts were conducted by people familiar with the ground and equipped to carry out the crimes with speed and confidence. "It was calculated," said Second Lt. Peter Fluker, Company C's second platoon leader. "It was done with crowbars and heavy equipment and some sharp, blunt objects that were used to smash open big doors and jewelry cases. They were rescue workers of some sort."

In addition to the retail establishments that were clearly looted, other shops and newsstands were partly destroyed by localized collapses, and it was not clear yesterday if the scattered merchandise and open cash boxes inside indicated more looting or simple disarray. "In some places, you just can't tell," said First Sgt. John Brett, who spent several shifts on security duty in the dark basement, waiting in ambush with night vision equipment, hoping to catch returning thieves.

The scenes surrounding him were unthinkably bizarre.

At the northeast corner of 5 World Trade Center are the remains of a Borders bookstore with many of its windows blown out. Above it sits the blackened and twisted frame of the buildings, through which water drips on the stocked cases of best-sellers, including stacks of new releases. Only a few bookcases are knocked over. All are coated with dust.

An idled escalator leads down to the darkened basement, which has become an unsettling tableau of New York City at the moment that the destruction began. A walk through the Borders basement, past the travel section and a customer service counter, leads out to the main concourse, where untold numbers of commuters and shoppers mingled at the moment the first jetliner slammed into the complex.

The concourse is a world that stopped.

Inside Sunglass Hut International, an employee's breakfast � three link sausages and a moldy entree with a fork standing upright � rests on the counter beside the cash register. The newsstands still hold stacks of the papers from the morning of the attack. At the entrance to the Warner Brothers store, the plastic statues of cartoon characters � Bugs Bunny, the Tasmanian Devil � stand wide-eyed in the blackness, their faces leering as the beam of a flashlight swings by, their heads and backs coated with soot.

At the Chase A.T.M. booth, a customer's receipt � for a $100 withdrawal made at 8:51 a.m. on Sept. 11 � was protruding from the receipt slot. Captain Heintz removed it, blew off the glass fragments and dust, and placed it gingerly on the counter with a faint tap of his hand. "This is from one of the last poor people who was down here," he said.