Six days after the terrorist attack on the World Trade Center, much of downtown Manhattan opened for business Monday, even as thick smoke drifted from the pile of rubble where the majestic Twin Towers once stood.

But it was far from business as usual: Wall Street's foot soldiers — some carrying American flags, some wearing masks to ward off the smoke — were greeted by police checking identification.

National guardsmen in camouflage stood silently on some street corners, gripping semiautomatic rifles.

The missing haunted the streets: Homemade posters with smiling faces stared from telephone poles and restaurant windows.

Blocks away, the rescuers continued the desperate work of sifting the wreckage of the Trade Center, hoping to find survivors among 4,957 missing souls. Around 300 of the missing are firefighters.

After a two-minute silence — and a trading-floor chorus of "God Bless America" — a group representing New York's rescue workers rang the opening bell at the New York Stock Exchange.

"We're going to stick our thumb in the eye of the murderers," Treasury Secretary Paul O'Neill at the NYSE building Monday where an American flag was draped over the entrance.

"Tuesday was such a nightmare, people covered in ash, people crying, people not knowing what was going on," said Shannon Jeffries, 32, on her way to work Monday at JPMorgan Chase. "I haven't been back to work since, and I'm not sure what to expect."

Harvey Grossman, a state Insurance Department employee, emerged from a subway station in lower Manhattan and had to show two forms of identification to walk on the streets.

"Then I went through a second checkpoint which is OK with me," he said. "They can stop me a half a dozen times if they want to. It's for my safety."

The confirmed death toll from Tuesday's terrorist attacks on the World Trade Center towers hit 190. On Sunday, rescuers reached a train platform 80 feet below the center's remains but found no survivors.

Monday was a day for reopenings. Besides the markets, City Hall, other government buildings and courthouses opened their doors.

"The life of the city goes on, and I encourage people to go about their lives," Mayor Rudolph Giuliani said Sunday.

They just had to step carefully. The narrow streets of the city's southern tip — home to the city's financial and government sectors — were crisscrossed with heavy utility cables. Portable generators hummed on sidewalks. Telephone and electric service was spotty.

The Wall Street subway station was closed, and only subways on the east side of downtown Manhattan were running. A new ferry service carried passengers across the East River from the borough of Brooklyn. Streets are closed to vehicles and some thoroughfares are blocked altogether.

Telephone and electric service were spotty; police headquarters was among the places with phone problems on Monday morning.

Preparations for this day had been difficult, and fraught with emotion.

Felix Fajardo mopped the foyer of a Wall Street law firm Sunday, trying to clear off the film of fine gray dust that spread for blocks, sticking to shop windows, ATMs, awnings — "all over the place."

Dennis Goin, president of Goin & Co. brokerage firm, planned to sleep at his office down the street from the NYSE building, just to be ready for what he feared would be a financially tumultuous and emotionally searing day.

"You might be calling to people ... who you might call once a month, and when you place that call, you might be told that Joe isn't here anymore," Goin said.

There was scant room for hope that all those missing Joes would be rescued.

"The recovery effort continues and the hope is still there that we might be able to save some lives. But the reality is that in the last several days we haven't found anyone," Giuliani said.

No survivors have been pulled out since Wednesday, and Giuliani said that most of what rescuers found was body parts, not bodies.

Among the grisly finds have been a pair of hands, bound together, found on a rooftop. Another was the torso of a Port Authority police officer, identified by the radio still hanging from his belt.

James Monsini, a volunteer and demolition expert from Brockton, Mass., said he and some fellow workers were concentrating on subbasement level garages and shops. He said they were hoping for air pockets that would allow victims — perhaps trapped in their cars — to breathe.

"I saw a car with an interior light on, and I got really hopeful that it was a sign (of life)," he said. "But the person was dead."

On Sunday, rescue crews for the first time penetrated into the lowest underground level beneath the towers, to the New Jersey commuter train station 80 feet down. They found gaps in the debris but not one survivor.

"In my opinion, I don't think we are going to find anyone alive," U.S. Marshal Paul Stapleton said. "This is worse than an earthquake."