SANTA ANA — In the squalor of Orange County's poorest neighborhoods, an ancient and endangered people is battling cultural extinction.

They are Indochinese Muslims who call themselves the Cham. For more than 1,000 years, they ruled the kingdom of Champa in what is now southern Vietnam. Overrun by the Vietnamese, many fled to Cambodia, where they clung to their distinctive language, culture and faith. After the communist takeover in 1975, the Cham and other minorities were singled out for persecution by the Khmer Rouge.

Today, about 132 refugee families have settled in Orange County, the largest Cham enclave in the United States.

They live tightly clustered around mosques in Santa Ana and Fullerton, praying to Mecca five times a day and teaching their daughters to cover their heads chastely. Cham elders boast that in 10 years in the United States, they have not lost a single child to crime, gangs, drugs--or assimilation. Most marriages are still arranged, with young people strongly encouraged to marry other Cham and forbidden to marry non-Muslims.

"Our community is better because our people follow strict Islamic rules," said Dollard Phar, an elder in the Santa Ana mosque. "No adultery, no robbery, no drugs, no gangs, no drunks."

Try as they may to hold on, the Cham see some of their customs slipping away. Daily life in modern and individualistic Orange County challenges every aspect of traditional Cham culture.

Former peasants, fishermen and blacksmiths work in automated factories, but some dutifully pray inside their parked cars during lunch breaks. Their children circumnavigate the permissive world of Southern California schools and malls, then come home to study the Koran.

This clash between cultures creates new and baffling choices. Among the starkest is whether this closely intermarried community should change its marriage customs in light of a newly discovered genetic disease that is killing some of its children.

One Santa Ana couple, who are first cousins, have lost five of their seven children. They are expecting an eighth child. So far, they have shunned Western medical intervention, including prenatal tests that would detect the disease.

"We know science does a lot of things that are perfect," explained Phar. "But we let things go with God."

Since the 19th Century, the few scholars who have noticed the Cham have mainly portrayed them as a vanquished and vanishing race.