LONDON — It was a quiet, jittery morning, one that had become too common.

More than 6,000 police officers blanketed London yesterday, four weeks after blasts shattered subway cars and a bus, two weeks since a second attempt to bomb the Underground, the subway system. Commuters streamed past bomb-sniffing dogs. They hurried beneath sniper scopes, studied the faces of people around them. They wriggled in their seats and some swallowed hard when trains clattered away from platforms and roared through tunnels toward the next stop.

It was a morning to cope, a morning of new threats. Many Londoners feared militants would strike again on the four-week anniversary of the deadly July 7 attack. The rush hour was uneventful, but then came another jolt. In a videotape broadcast yesterday, Ayman al-Zawahri, Osama bin Laden's lieutenant, told Britain that Prime Minister Tony Blair's support of U.S. policies in the Middle East had "brought you destruction to the heart of London, and he will bring you more destruction, God willing."

The ride out of London was more nerve-wracking than the journey in.

The city's Piccadilly subway line reopened stops that had been closed by bomb damage. But many commuters chose alternate routes, bypassing the yellow fluorescent jackets and the black guns of police. Since July 7, when four bombs killed 56 people, including the four bombers, and left grainy photos of militants lingering on TV, subway riders have dropped by 30 percent on weekends and up to 15 percent on weekdays, according to the city's transportation service.

"I was on the Tube [the subway], and a white guy next to me was staring at a dark-skinned guy," said Anetta Bentley, a shop worker in Notting Hill. "The dark-skinned guy look at him and said, 'Why you looking at me? Why you looking at me? You want to check my rucksack?' But everyone was looking at him and his rucksack. We couldn't help it. It's strange and not easy getting back to normal."

Above the Covent Garden subway stop, Ismael Abdurahman, 23, appeared in Bow Street Magistrate's Court. He blew a kiss to two women in the gallery and became the first suspect indicted in connection with the July 21 failed bombings of the same subway system. He is charged with withholding information that allowed alleged bomber Hamdi Issac to escape to Italy.

"The defendant will be contesting the charge as he has no involvement in any terrorist activity whatsoever," said Abdurahman's lawyer, Anne Faul. Judge Timothy Workman denied bail and Abdurahman, facing a maximum penalty of five years in prison, waved again to the two women, one of them weeping, before he was led away. Two other suspects were charged later in the day with the same offense of withholding information on the alleged attackers, according to the BBC.

The subways rattled on. Double-decker buses meandered through traffic, past Hyde Park and Kensington Gardens, skirting the fringes of Buckingham Palace. Cellphones rang, tourists unfolded maps and the largest police presence in decades gripped the city. Richard Moss, an electrical-engineering student, walked with a backpack on an overpass above rusty train tracks. He knew that July 7 and July 21 were both Thursdays and wondered what would happen this Thursday.

"Some Londoners are apprehensive. Others are moving forward and getting on with their lives," he said. "But we're doing these things individually. We've somehow lost a sense of community. Instead of cultures coming together and fusing, we're doing it all apart and we've got to stop that.

"I'm not scared to take the subways or buses, but my girlfriend is. She has that sense of not being sure. You used to know what terrorists looked like, but now they look like everybody. My uncle lives about 10 minutes that way [he pointed west] and two of the guys they arrested in the bombings lived right next door to him and he didn't even know."

Los Angeles Times staff writer Janet Stobart contributed to this story.