As they consider the suicide bombing that recently rocked their country, many Swedes have taken comfort from the attack’s most enduring image, as captured by a security camera: a man in a red jacket kneeling by the dying bomber, asking if there was anything he could do for the man while other bystanders, spying unexploded pipe bombs still strapped to the man’s waist, backed away, shouting, “Bomb! Bomb! Bomb!”

As Swedes sigh in relief at the failure of the attack on Saturday that seemed intended to cause mass casualties among Christmas shoppers, they have taken comfort from that aspect of an otherwise shocking scene. Many have described it as exemplifying the compassion and tolerance Sweden prizes as part of its national character — qualities, they say, that must not be surrendered in a new era of terrorist threats.

On Wednesday, the Swedish security police released a study of Islamic extremism that was commissioned months ago, but released now to allay public disquiet. A summary said the study had concluded that “the terrorist threat in Sweden” involves fewer “than 200 radicalized individuals,” that “they pose no serious threat to the society and government” and that Sweden’s response should be confined to “preventive measures” — and, by implication, not broader social or political changes.

Under questioning, officials said that Taimour Abdulwahab al-Abdaly, the Iraqi-born Swede who the police say was the perpetrator and the only person to die in the attack, was not among the 200 people under surveillance before the bombing. That disclosure was likely to raise fresh questions about the grasp the Swedes have achieved as they monitor extremism among the country’s 400,000 to 500,000 Muslims.

One view among diplomats is that the Swedes’ tolerant attitude may have left the security establishment unprepared for the bombing, the first by Islamic extremists in Scandinavia.

A resolve not to let the bombing wrench the country from its moorings has been evident in Prime Minister Fredrik Reinfeldt. “This is not the path we want to go down,” he said in his initial response to the bombing. “Sweden is an open society which has demonstrated a will that people must be able to come from different backgrounds, believe in different gods, or not believe in any god at all — and be able to live side-by-side, together.”

But even as investigators seek the accomplices they believe Mr. Abdaly may have had in Sweden, Britain and the Muslim world, a national debate has begun over the whys, as well as the hows, of the attack. Among the questions are these: Why has the culture of suicide bombing come to Sweden, when it has been one of the most generous countries in Europe in opening its doors to Muslims fleeing war and repression? And why now, when the country has looked on for years as other European capitals, notably London and Madrid, have been the targets of deadly bombings?

And why, too, did such a sharp turn come in the life of Mr. Abdaly, who came here as a 10-year-old, his family fleeing the oppression of Saddam Hussein, and gained a reputation in Tranas, the small town where his family settled, as a quiet, well-mannered and amiable boy?

One elected official who thinks the time has come for Sweden to get tough, whatever the cost to its tolerant reputation, is Jimmie Akesson, the leader of a right-wing party, the Sweden Democrats. In a September general election the party campaigned on a program calling for a 90 percent cut in immigration. Sweden’s migrant population has soared in recent decades, changing one of the most ethnically homogeneous populations in Europe.

Mr. Akesson, whose party won 20 seats in the 349-seat Parliament, said in an interview that the bombing was predictable, considering the unassimilated lives of most Swedish Muslims. “Up to now, other parties have just laughed at us and said there is no serious threat from extremist forms of Islam in Sweden, but now we know there is,” he said.

Mr. Akesson argues that Sweden’s approach to multiculturalism has left many Muslims unable to speak Swedish, unreconciled to Swedish laws and mores that conflict with Islamic beliefs and clustered in what amount to ghettos in big cities like Stockholm, Malmo and Gothenburg.

“They must adapt to Swedish society, instead of Sweden adapting to them,” he said.

On Drottninggatan, the crowded pedestrian mall where Mr. Abdaly attacked, many shoppers walked briskly past when asked to discuss the issue, shaking their heads as if the bombing were too distasteful to consider. But one man who paused said Sweden would have to adapt and become more “realistic” in its policies by assimilating newcomers better.

“Should we now shut the door?” said the man, a 55-year-old businessman who gave only his first name, John. “Absolutely not. We have benefited far too much from the foreigners who have come here to do anything like that.”

Some Muslims condemned Mr. Abdaly. Abdul Rauf, a 30-year-old from Pakistan with a spiky black beard poking from a hooded parka, said of Mr. Abdaly, “You have to be mad to do something like that.” Had Mr. Rauf, with his Islamic-style beard, been hassled over the bombing? “Not at all,” he said. “Swedish people are very polite, very kind.”

But his was not a universal view. Masoud Kamali, a professor of social work who wrote a multivolume report on discrimination in the country, said Sweden lived an illusion in seeing itself as the world’s fairest, least discriminatory society.

“When I travel to the United States, people are always saying, ‘Oh, Sweden is very tolerant, very open,’ ” said Mr. Kamali, who arrived from Iran in the 1970s. “It’s an established myth. But it’s not.”

Mr. Kamali said Sweden would have to take radical steps to decrease the segregation and marginalization of Muslims, or face what he described as “many burning areas” across the country. He said Swedish governments had followed a social democratic model of equality for decades, emphasizing barriers of class and gender, but ignoring or underestimating the force of ethnic and religious bias.

“It’s a question of belonging,” he said. “Are you accepted as you are, living as a true Muslim in a modern European country?

“The answer is no, so you have to find something else, and he found the bombing.” He added, “And I can promise you this, it’s going to happen again.”