PROVO — Every Wednesday, hundreds of young Mormon men and women not far removed from high school arrive on the campus of Brigham Young University, where they are severed from family and text-messaging and entrusted with the very future of their faith.

Sequestered in classrooms for 14 hours a day, these missionaries-in-training are taught to boil down core doctrines to make them understandable and consistent, whether their audience is in Utah or Uganda.

But increasingly, classroom conversations at the LDS Church's flagship Missionary Training Center have centered not just on winning new believers but on keeping them — a topic looming as a critical challenge for whoever is picked to succeed church president and prophet Gordon B. Hinckley, who died Sunday at 97.

Although retaining members is a challenge for all evangelizing faiths, the LDS Church appears to have a particularly poor retention rate in some countries.

The foreign retention rate is critical to the future of the LDS Church. An American-born denomination, The Church of Jesus Christ of Latter-day Saints now boasts more members abroad than at home — about 55 percent of the world's 13 million Mormons live outside the U.S., according to church figures.

The Mormons are working hard to maintain doctrinal integrity and still compete in the spiritual marketplace for converts. The effort is playing out at the Missionary Training Center, which is equal parts language lab, college dorm and proselytizing think tank.

The largest of 17 such centers around the world, the 4,000-capacity Provo MTC trains young men and women for three to 12 weeks. The length of stay depends on whether the missionary is learning one of the 53 languages taught here and its degree of difficulty.

All able Mormon men are expected to embark on a two-year mission at 19. The center's halls teem with polite young men who wear dark suits and washable polyester ties they swap like trading cards in the mission field. There is a smattering of women preparing for 18-month trips.

The closest thing to a student union is a basement laundry room, where missionaries on their day off, or Preparation Day, relax in jeans and sweat shirts and write weekly letters home. Or they can send e-mail, though no more than 30 minutes on the Internet is allowed.

Brock Hale of Medicine Hat, Alberta, described training that goes beyond the language and doctrine he needs to engage potential converts in Romania.

His teacher, a returned Romanian missionary, provides crucial cultural advice: Be prepared for the difficulty of selling Mormonism's prohibition against smoking, and don't be easily offended by Romanians, who are bold and quick with insults.