WASHINGTON -- One in four younger U.S. Muslims say suicide bombings to defend their religion are acceptable in some circumstances, a poll says.

However, most Muslim Americans overwhelmingly reject the tactic and are critical of Islamic extremism and al-Qaida, according to a survey by the Pew Research Center.

The survey, one of the most exhaustive ever of the country's Muslims, revealed a community that in many ways blends comfortably into society. Its largely mainstream members express nearly as much happiness with their lives and communities as the general public does, show a broad willingness to adopt American customs, and have income and education levels similar to others in the U.S.

But the survey revealed noteworthy pockets of discontent.

Although nearly 80 percent of U.S. Muslims say suicide bombings of civilians to defend Islam cannot be justified, 13 percent say they can be, at least rarely.

That sentiment is strongest among those younger than 30. Two percent of them say it can be justified often, 13 percent say sometimes, and 11 percent say rarely.

Ahmad Al-Akhras, a Columbus resident and national vice chairman of the Council on American-Islamic Relations, expressed concern over any support for terrorism, particularly among younger Muslims, but he called the number small.

"There is no justification in Islam for targeting civilians or supporting terrorism. Those who commit these actions are committing a sin," he said. "Muslims believe that human life is sacred and that it is protected."

Al-Akhras, who also is president of the Islamic Foundation of Central Ohio, said that Americans in general might be more supportive of targeted attacks on civilians, as part of the war on terror, than U.S. Muslims.

A December 2006 poll by the University of Maryland-affiliated WorldPublicOpinion.org found that 24 percent of Americans think bombings or other attacks intentionally aimed at civilians are "sometimes or often justified."

Jordan Robinson, 22, a Muslim from Gahanna, said the survey shows most American Muslims are "mainstream" but that it points out a need to address the grievances of young Muslims.

"In any population, there's always going to be a fringe that does support radical, extreme reaction," said Robinson, an Ohio University journalism major and former vice president of the OU Muslim Students Association.

Too many Americans continue to buy into the myth that Muslims support acts of terror in the name of the religion, he said.

Radwan Masmoudi, president of the Washington-based Center for the Study of Islam and Democracy, which promotes the compatibility of Islam with democracy, said support for terrorism among younger Muslims was "a hair-raising number."

Even so, U.S. Muslims are far less accepting of suicide attacks than Muslims in many other nations. In surveys Pew conducted last year, support in some Muslim countries exceeded 50 percent, while it was considered justifiable by about one in four Muslims in Britain and Spain, and one in three in France.

In other findings of the U.S. Pew study:

• Only 5 percent of U.S. Muslims expressed favorable views of al-Qaida, though about a fourth did not express an opinion.

• Six in 10 said they are concerned about a rise in Islamic extremism in the U.S., while three in four expressed similar worries about extremism around the world.

• Yet only one in four considerd the U.S. war on terrorism a sincere attempt to curtail international terror. Only 40 percent said they believe Arab men carried out the Sept. 11 attack.

• By six to one, they say the U.S. was wrong to invade Iraq, while a third say the same about Afghanistan -- far deeper than the opposition expressed by the general U.S. public.

Dispatch reporter Randy Ludlow contributed to this story.