Seven bullets fired into a young Brazilian man's head by an undercover policeman who mistook him for a suicide bomber have set off an impassioned debate over the rights and wrongs of anti-terrorism tactics and racial profiling in one of the world's most ethnically diverse cities.

Ajmal Masroor, the 33-year-old director of a community relations group here, is a highly educated and articulate Muslim of Bangladeshi origin who is welcomed as a consultant and adviser in the corridors of power. Yet when he walks the highly patrolled streets of the Whitehall government sector these days, he said, he thinks twice because police have adopted a shoot-to-kill policy against people they deem to be active terrorists.

"I am a young Asian man with a beard and a rucksack on my back and I'm thinking, am I going to be the next target?" he said, addressing a terrorism conference Tuesday at the Royal United Services Institute. The men who struck the London transit system this month all hid their bombs in such bags.

At the same session, a senior police official of South Asian ethnic origin who would not allow his name to be used said he felt queasy when "two colleagues of the firearms branch saw me running up the road with my rucksack on."

Yet after facing two coordinated bombing attacks on the city's transit system -- one of which killed 56 people, including the bombers, and injured 700 -- many people say they understand the reasons for the policy. "Shoot-to-kill keeps us secure, and I feel protected, but at the same time I'm scared," said Angel Henry, 22, an airline employee who is part Jamaican and says that at times she feels singled out for having black features. "It's a Catch-22 situation. We've got to just ride it out."

Jean Charles de Menezes, a 27-year-old electrician who had lived in London for three years, was gunned down execution-style -- seven bullets to the head, one to the shoulder -- in front of horrified passengers in a subway car standing Friday morning in London's Stockwell station. The officer firing at him presumed he was about to detonate a bomb after he ran from pursuing police. But as it turned out, Menezes had nothing to do with terrorism, as police conceded over the weekend.

Beyond the killing itself, what shocked many Londoners was the discovery that Menezes had been killed under instructions that had never been publicly articulated, which allow officers to shoot in the head someone they believe is about to commit a suicide bombing. Code-named Operation Kratos, the policy was put in place after the Sept. 11, 2001, attacks in the United States.

"Shoot first and ask questions later is what we've heard happening in Iraq," Masroor said. "It's not what we expected to happen here."

Former police commissioner John Stevens stunned many over the weekend when he wrote in a newspaper column that the policy had been imported from Israel, where the authorities had drawn a stark conclusion: "There is only one sure way to stop a suicide bomber determined to fulfill his mission: destroy his brain instantly, utterly."

Ian Blair, Stevens's successor as police commissioner, further fueled the debate when he told a Sky television interviewer that, despite his deep regrets over Menezes's death, the same thing could happen again.

The ensuing debate has not followed the usual political divide here. London Mayor Ken Livingstone, who usually is far to the left of Prime Minister Tony Blair's government, has urged understanding for the police. "Consider the choice that faced police officers at Stockwell last Friday -- and be glad you did not have to take it," he wrote in Monday's Evening Standard.

But Tim Hames, a conservative columnist for the Times newspaper, urged a reexamination. "There is a world of difference between a plainclothes policeman finding himself riding on the Tube and spotting a man with a large bag behaving in a manner that makes him a potential suicide bomber and shooting him, and chasing a person onto a train carriage and firing at him," Hames wrote.

Some Londoners were not aware that a record number of police officers -- who once upon a time were famed for not being armed -- are now packing guns. According to the most recent figures, about 2,100 officers in London are licensed and trained in using submachine guns and pistols.

London has experienced terrorism before -- notably during a bombing campaign by the Irish Republican Army from the 1970s to the 1990s.

Chris Mullen, a Labor Party member of Parliament who until recently had a residence in south London, was a crusading author whose research in the 1980s helped free a half-dozen Irishmen wrongly accused of terrorist bombings in mainland Britain. Today, he says the threat is different: Irish terrorists often gave warnings before their attacks and never engaged in suicide missions.

Still, Mullen called last week's killing "a reminder that we have to tread very carefully. We have to bear in mind in giving extra powers to police that they do have a history of making mistakes."

Andrew Silke, a psychologist at the University of East London who has studied terrorism in Northern Ireland and the United States, said the public generally supports a harder line after terrorist attacks. "If you're a government, the most popular thing you can do is go out and kill terrorists," he said. "Most people will regard this death as a tragedy, but they'll be understanding and appreciative of what the police are trying to do."

Ian Blair and other top police officials have met repeatedly with Muslim leaders in recent days to explain the policy and plead for community support, which they say they must have to catch the would-be bombers, all of whom are believed to be Muslims. But many prominent Muslims warn that the shoot-to-kill policy could alienate the very people whose support the police need -- young Muslims.

"This is an Israeli model and it's a very dangerous model for London," said Ahmed Versi, editor of the weekly Muslim News newspaper. "We're getting many e-mails from young people who are worried. This is creating fear, and it is not helping the police."

Racial profiling by police has been a controversial issue here for decades. Under Britain's broad anti-terrorism laws, police can be granted "stop-and-search" powers to question anyone and, if they deem necessary, conduct a body search. Teams of officers can be seen at transit stations throughout the city scanning passengers. When finished questioning someone, they write out a form for the person that explains the reason for the stop and gives the shoulder badge number of the officer, in case the person wants to file a complaint.

Government statistics released last year showed that blacks were eight times more likely and Asians five times more likely to be stopped and searched by police than whites. Police officials have insisted they are doing all they can to curb profiling.

But young people at London's sprawling Victoria train station said Tuesday afternoon that they experience a different reality. "I don't run for a train or a bus anymore," said Chris Murray, 29, a drug counselor and youth worker. "I think for Asians in general, it's dangerous. I'm Asian, but I'm a Catholic and I was born in Britain. You find yourself feeling defensive in the train, people checking you out."

"I had a blue Nike bag I used to use, and I changed to a black Nike bag now because they were all blue," he said, referring to the bags used by the suspects in last week's abortive bombings.

Henry, the black airline employee, who was waiting for a train with friend Germaine Ghent, said that at times she wants to lash out at Pakistanis and Muslims in general. "In a way, I'm so angry that I feel like everybody of that race and gender should be rounded up and shipped back home, but then I realize that's wrong and innocent people would be caught up in it," she said.

As she was speaking, police officers a few yards away stopped a slightly built young Indian man in a blue suit and tie. Bystanders watched as they rifled through his two shopping bags and checked the red-and-white sport bag slung across his back. Police asked him to stretch out his arms, and he obliged while they publicly frisked him.

"That's so humiliating," said Ghent, who also is black. "I feel sorry for him."

The police officers handed the man a report written on a pad, and one of them bid him a polite farewell loud enough for bystanders to hear: "Have a safe day. Nice meeting you. All the best. Take care."

The man nodded and hurried for the subway.

Two men stop by London's Stockwell subway station to look at a memorial to Jean Charles de Menezes, the man mistakenly shot and killed by police.