MOSCOW - Passengers daydreamed, dozed and struggled to sober up. Couples clutched each other and nuzzled. Children dangled their feet. One rider sipped a silver can of Baltika beer.
It looked almost like a typical Sunday on Moscow's noisy, stuffy and usually crowded subway, better known as the Metro, but the bombing Friday that killed 39 passengers and injured more than 130 was still making itself felt.
The system ran almost as it always does. The trains, painted sea and sky blue slid into stations with a deep-throated roar. Brakes screamed. Soot-blackened electric cables snaked past within inches of the windows.
Thousands of pairs of boots and shoes echoed over yellow-stained marble floors. Mosaics of heroic workers and stained-glass renderings of the Soviet era's Red Star greeted riders at central- city stops. Passengers leaned against doors printed with the warning: "Don't Lean Against."
But tension lay just beneath the surface. In one car yesterday, riders uneasily eyed a young man standing near a large black sports bag. No one summoned up the courage to ask him if it was his. No one wanted to risk sounding afraid.
A woman in a fake fur coat and purple scarf sat motionless in car No. 7369 on the system's Circle Line, which loops the central city, her head tilted back and her mouth open. Another woman felt her neck for a pulse. She pinched the woman's nose, pulled her lapels and finally slapped her awake, telling her to get out at the next stop.
The woman, apparently drunk, looked around. None of the other passengers looked back. She shuffled off at the next stop.
At Paveletskaya Station, where the bombed train was heading Friday, a police officer gripped a portable metal detector and watched the scores of passengers carrying bags and boxes on the escalators heading to and from the trains. Over the stretch of a few minutes, he neither stopped nor searched anyone.
"We use face control," he explained. "If a person looks nervous, we search him."
Police have tried to guard the system since 1997, a year after a bomb planted near the Tulskaya Station killed four people and wounded 12. The second-deadliest bombing in the system was a 1977 attack by Armenian separatists, who killed seven and injured 32.
But protecting the labyrinthine system would seem nearly impossible. Almost 9 million riders use the subway each day, and almost every other passenger yesterday carried a shopping bag, a backpack, a box, a gym bag or a suitcase - all potential hiding places for an explosive.
At Paveletskaya Station, where two lines cross, a waist-high wall in the middle of the Green Line platform had become a makeshift shrine. Dozens of red, purple and white long-stemmed carnations lay atop the white marble. From time to time, waiting passengers paused to light candles. The gusts from passing trains kept extinguishing the flames.
Anna Kalinetskaya, a 40-year- old government worker in a white fur coat, took six red carnations out of their newspaper wrapping and laid them by the others. On an arch overhead, a brass hammer and sickle gleamed in the murky light.
She didn't know any of the victims, but that didn't matter.
"This could happen to anybody," she said. "I don't know what will happen now. You never know when something like this will hit you. Even your house can blow to pieces. Or you can get blown up on a bus."
Ludmilla Adler, a 30-year-old housewife with a 1-year-old child, looked at the shrine and noticed something disturbing. Someone had written on the wall in blue, "We Will Take Revenge." Next to the words was a drawing of a gun sight.
Adler, who is Jewish, a tiny minority in Russia, began to rearrange the flowers to hide the words. Tears formed in her dark green eyes.
"Who, exactly, should they take revenge on?" she asked. She expressed the fear that ultranationalists would look for scapegoats. "Maybe they will wind up getting someone who had nothing to do with this."
Russia's Federal Security Service, the successor to the KGB, said the explosion Friday was more likely an act of terror than an accident.
If so, it was the deadliest bomb attack in the history of the Metro and the worst assault here since October 2002, when 41 Chechen separatists stormed a Moscow theater and seized about 700 hostages. At least 129 hostages and all of the guerrillas died during a rescue effort by Russian special forces.
Russian President Vladimir V. Putin, without providing any evidence, blamed Chechen separatist leader Aslan Maskhadov for the subway bombing, and ruled out peace talks with the rebels.
A Chechen envoy, Akhmed Zakayev, issued an open letter yesterday denying responsibility and condemning the attack. He warned that continued fighting in Chechnya could lead only to more "animosity ... and terror."
Police suspect the blast was the work of a suicide bomber rather than someone who left an explosive on the train. Mayor Yuri Luzhkov said the explosive detonated about 20 inches off the floor, indicating that someone had been holding it.
If true, it was the third major suicide bombing in the capital in eight months. Two Chechen female suicide bombers killed 14 people at a rock concert in July. In December, a Chechen woman detonated an explosive in front of the National Hotel, across the street from the Kremlin, killing herself and five others.
Perhaps because history has dealt them so much sorrow, Russians are known for their stoicism. But Adler says that they are nearing the limit of what they can absorb.
"People don't have the answer to this, they don't know how to confront it," she said, standing next to the improvised shrine at Paveletskaya Station. "Fear is seeping deep, and life cannot go on as it has."