But based on the fund-raising he conducted before this year, Romney's other sectors of support are likely to be dwarfed by the backing he is receiving from LDS members. Wealthy Mormons giving to Romney's PACs include the Marriotts, the Bethesda, Md.-based hotel family, who have given more than $390,000; the family of Jon Huntsman Sr., the owner of a major Utah chemical company, which has given more than $170,000; and the family of Utah Jazz owner Larry H. Miller, which has given $100,000.

Also giving heavily have been thousands of rank-and-file church members. After Romney last fall sent direct-mail solicitations to Republicans nationwide, his two biggest state-level PACs received 319 checks from Utah, which is about two-thirds Mormon — a third of the total number of checks he received in the year's final quarter. In the same period, he received seven checks from Massachusetts, where he has lived more than 30 years.

After Utah, which holds a quarter of the church's 5.7 million U.S. members, the highest concentrations of Mormons are in Idaho, Wyoming, Nevada and Arizona, in that order. California, by virtue of its size, has the second-largest Mormon population in absolute terms — about 750,000.

While the church is strongest in the West, it is represented in almost every corner of the country, in congregations organized into "stakes," "wards" and "branches." Its hierarchy is headed by a president and two counselors and a Quorum of the Twelve Apostles, while congregations are led by laymen, a role Romney served.

Church leaders encourage members to vote and be involved in politics, and they occasionally weigh in on "moral" issues such as ballot initiatives on same-sex marriage or gambling. But to preserve the church's tax exemption, its leaders warn against making endorsements inside churches or using membership lists or the church's Web site for partisan purposes.

Romney's campaign edged against these boundaries last fall when Kem Gardner, a Utah developer whose family has given $140,000 to Romney's PACs, set up a meeting in Salt Lake City with a church apostle, a Romney consultant and one of Romney's sons. Documents obtained by the Boston Globe showed that the apostle, Elder Jeffrey R. Holland, suggested promoting Romney via the alumni association of the business school at church-owned Brigham Young University, a group with 5,500 members in 40 chapters.

Days later, two deans from the business school sent an e-mail rallying support for Romney to 150 members of the school's advisory council and 50 chapter leaders of the alumni association, the Management Society. Because it is legally part of church-owned BYU, the society is also prohibited from backing candidates. After the Globe reported on the efforts in October, church leaders disavowed any campaign on Romney's behalf.