Albert Siriboe is a black man in his twenties who lives south of the Thames River, which he said means he is likely to be stopped by police at any time for no reason. "The attitude of police is if one black person is a bomber, then we are all bombers," said Siriboe, 26, a sales clerk who said police often accost him as he walks to work or drives his car.

Siriboe's complaint is a common one in his south London neighborhood of Stockwell, where many residents are from Africa and the Caribbean. Many people in Stockwell said they were saddened but not surprised when police shot and killed Jean Charles de Menezes, a 27-year-old Brazilian electrician, in the Stockwell subway station as they hunted a suspect linked to last month's London transit attacks.

Menezes' death and complaints about police bias in minority communities are focusing attention on Scotland Yard, which has been struggling to live down the reputation of being branded "institutionally racist" in a watershed independent report in 1999. That report spurred the Metropolitan Police Service, Scotland Yard's official name, to start a major recruiting drive to shape a more diverse force. The percentage of black or minority officers on the 31,500-member force has risen from 3.4 percent in 1999 to 7.2 percent, according to official statistics.

Stockwell and nearby Brixton are among the most racially mixed neighborhoods in London, where Asians and blacks combine to make up about a quarter of the population of 7 million, according to government statistics. Racial tensions have flared repeatedly south of the river, especially during riots in Brixton in the 1980s and 1990s, and many people are deeply suspicious of the police.

Siriboe said the situation worsened last month, after a July 7 attack on three subway trains, which killed 56 people, including four presumed bombers, and an unsuccessful bombing July 21. The four bombers and five people charged in the failed attempt were young men who were either dark-skinned immigrants or sons of immigrants from Africa and Asia.

"Relations have never been good, and what is going on now doesn't help," Siriboe, who moved to Britain from Ghana about 15 years ago, said of his experience with police searches. "They are stopping me for who I am. It's frustrating. I am trying to put myself in their situation, but I can see why so many minorities are angry."

At the Shapes 2 barbershop in Stockwell, which caters to black customers, people listening to Siriboe's complaints nodded in agreement. Human rights and citizens groups who monitor police activities report evidence of a far more aggressive stop-and-search policy since the bombings, and they said people of color were the most frequent targets.

Police apologized for shooting Menezes seven times in the head, saying the July 22 killing was a mistake in the tense days following the subway and bus attacks. Since then, neighbors have been laying flowers and notes at a makeshift altar in his honor at the subway entrance, with many messages that lash out at the police, including one that reads, "Innocent life destroyed by a trigger-happy racist cop."

British police have long had broad powers to stop and search people on the street. Those powers were extended under anti-terrorism laws enacted after the Sept. 11, 2001, attacks on the United States. Since last month's bombings, it has become even more routine for London police to stop, question and sometimes search anyone they consider suspicious. Officers who conduct such searches are required to provide a form and badge number, which can be used if those stopped want to file a complaint.

Scotland Yard says it does not engage in racial profiling. Police Commissioner Ian Blair said at a news conference this month that the department's stop-and-search policy is strictly "intelligence based." "If we said that the only people we were going to search would be young males of African, Caribbean, Asian or North African appearance, it would be handing the objectives to the terrorists, and they would immediately change their tactics," Blair said. "On the other hand, officers are aware of the suspects so far, and will act accordingly."

But Ian Johnston, the chief constable of the British Transport Police, a separate agency, was more candid in a recent newspaper interview, when he said his officers would not be "wasting time searching old white ladies" for bombs.

Transport police statistics show that seven times as many people were searched in July than in June, and that nearly double the percentage of Asians were being stopped after the bombings.

The aggressive police work in the past month has been a comfort to many Londoners. Police supporters measure success with results: Five men accused of carrying bombs on July 21 are now in jail, along with many others accused of helping them or hindering the police investigation.

"Most people are delighted," said Kate Hoey, a member of Parliament who represents the area that includes Stockwell. She said older residents were especially happy about the visible police presence and believed it directly helped them by deterring burglaries and other crimes.

In recent years, she said, police have made a concerted effort to reach out to her constituents. "White kids are also fed up" with stops and searches, she said, and as officers get to know neighborhoods better, the numbers could decrease. Blacks and other minorities account for 15 percent of recruitment classes at Scotland Yard, according to police figures. A police spokesman said officials want the police force to match London's ethnic mix.

But racism in the police force is still a major problem, according to Helen Shaw, co-director of Inquest, a nonprofit group that provides legal aid to the families of those who have died in police custody. "If you are a young black man in London, you are likely to have been stopped," she said. "People are outraged and tired of it."

In random interviews of black and minority people on a recent day in Stockwell, almost everyone described being stopped by police, many more than once, some dozens of times this year. They said typical reasons given by police were that they were wearing a similar sweat suit to a suspect or to remind them that their headlights were not on, even if it was barely dusk.

Reza Moghaddam, 16, said he had been stopped by police at least 10 times this year, often when he was on his bicycle. He said he did not want to waste his time waiting to receive the form that police are supposed to provide after a stop. "You get the feeling you are being bullied by them," he said as he sat on the wall of the Stockwell skateboarding park. A few dozen youths rode their bikes and boards up and down a paved area shaped like a moon crater. "I don't like the police," said Moghaddam, who said he was born in Britain and his father was from Iran.

One man, interviewed as he walked out of the Stockwell mosque, a run-down, two-story building across from a police station, said he thought that Muslims in particular were being watched. "It's just life now," he said, declining to give his name. He said he had been stopped many times and that being polite and looking officers directly in the eye made things go quicker and easier.

Damian Brown, 19, was more upset, saying he felt harassed as a black Muslim. Chatting with friends at Mother's Touch juice bar, the student said he had been stopped about seven times recently. Sometimes, he said, if he is with other young men, "police just follow to intimidate." Other times, he said, "They stop you, saying, 'You fit a description of someone we are looking for,' and I say, 'What description would that be?' "

A poster in central London urges the resignation of police commissioner Ian Blair and Prime Minister Tony Blair.

British-born Reza Moghaddam, 16, says he has been stopped by police at least 10 times this year, often when he was on his bicycle.