The release of a landmark report Thursday in Washington on the rapid growth of Islam touched off a national debate among scholars over its claim that there now are 7 million Muslims in the United States.
No one disputes that Islam is growing nationwide. In southeast Michigan, the number of mosques has more than doubled since 1991 from 17 to 39 and several are planning to expand into new, multimillion-dollar facilities.
Islam's political influence also is expanding and the release of "The Mosque in America: A National Portrait" was sponsored by the most-active Muslim lobbying group in Washington, D.C., the Council on American-Islamic Relations.
On Thursday, Ibrahim Hooper, the council's spokesman, said that his group henceforth will tell political leaders that 7 million is a "conservative estimate" of the U.S. Muslim population.
In sharp contrast, pollster George Gallup Jr. said, "These figures they are reporting are much exaggerated."
In Albany, N.Y., Seymour Lachman, one of the nation's top researchers of religious population over the past decade, said, "The figures are inaccurate and the political agenda is irresponsible."
Based on their survey research, Gallup and Lachman said the Muslim total is likely about one-third of the council's estimate.
In recent days, two scholars connected with the report have distanced themselves from the council's number.
The head of the highly respected Hartford Institute for Religious Research in Hartford, Conn., which cosponsored part of the research, said this week that Hartford was not endorsing any claims about total adherents.
The Muslim research was part of a much-broader survey on religious life in America -- a survey that was never designed to calculate membership totals, said Hartford director David Roozen. "There was nothing in the survey or in any of our group discussions about extrapolating total numbers."
Even as the report was being released, one of its coauthors -- Georgetown University sociologist of religion Paul Perl -- said he was more comfortable with an estimate of 2 million followers.
By late Thursday afternoon, the controversy led Hooper to declare flatly that the council believes most non-Muslim scholars are wrong about Islam's size.
"This gets irritating after a while. They don't know how to access the American Muslim community. We know how to reach American Muslims," Hooper said. "We talked to real live Muslims and asked them how many Muslims are out there. I am perfectly settled in my heart that we are accurate. Bottom line: Our numbers are better than their numbers."
The conflict put at least some Detroit-area Muslim leaders in the awkward position of defending the report even though their own numbers seem to dispute parts of it.
"I'm very comfortable with the number they gave," said Imam Mohammad Ali Elahi of the Islamic House of Wisdom in Dearborn Heights.
A major difficulty in estimating the size of Islam is that many Muslims are not active in mosques, said Imam Dawud Alim of Masjid Wali Muhammad in Detroit. "There is a larger inactive membership than an active membership, in this city anyway."
However, the new report's estimates of average mosque participation appeared larger than typical attendance numbers in Detroit mosques.
The report claims an average of 1,625 Muslims are associated with each mosque and an average of 292 people attend the Friday services that are the high point of the Muslim week.
In metro Detroit, a few mosques exceed the average, but some of the largest mosques report no more than 200 people at Friday services.
The size of the U.S. Muslim population has been a perennial puzzle. Unlike Christianity, Islam has not had an organized system of counting members. For years, national Muslim groups have declined to conduct a detailed census.
For the report, Muslim researchers interviewed spokespersons from 416 of the 1,209 mosques in the United States.
Most of the more than 160 questions in the survey were about congregational life, service projects, political involvement and views on American culture. One question asked for a broad estimate of how many people "are associated in any way" with the mosque, including children and people who might show up once a year.
The answer to that question was used to calculate a broad estimate of 2 million Muslims at least loosely connected with mosques. Then, the report's chief author, Ihsan Bagby, a member of the council's board, tripled that number to account for Muslims who have no contact with mosques.
"It's a guesstimate," Bagby said about his decision to triple the number. "The number sounds reasonable to me, but we do need more studies to finally pin down these numbers."