SPIRIT LAKE INDIAN RESERVATION, N.D. >> The man who plays Santa Claus here is a registered child sex offender and a convicted rapist. One of the brothers of the tribal chairman raped a child, and a second brother sexually abused a 12-year-old girl. They are among a number of men convicted of sex crimes against children on this remote home of the Spirit Lake Sioux tribe, which has among the highest ratio of sex offenders in the country.

Federal officials are now moving to take over the tribe’s social service programs, according to members of the tribe, government officials and documents. The action comes after years of failure by government and tribal law enforcement officials to conduct proper investigations of dozens of cases of child sexual abuse, including rape.

While members of the tribe say that sexual violence against children on the reservation is common and barely concealed, the reasons for the abuse here are poorly understood, although poverty and alcohol are thought to be factors. The crimes are rarely prosecuted, few arrests are made, and people say that because of safety fears and law enforcement’s lack of interest, they no longer report even the most sadistic violence against children. In May 2011, a 9-year-old girl and her 6-year-old brother were killed on the reservation after being raped and sodomized.

“It bothers me that it is so accepted, that it is considered so normal. It’s lawless,” said Molly McDonald, who was a tribal judge until March, handling juvenile cases.

The reservation has 38 registered sex offenders among its 6,200 residents, a rate of one offender for every 163 residents. By contrast, Grand Forks, N.D., about 85 miles away, has 13 sex offenders out of a population of 53,000 — a rate of about one in 4,000. In one home on the reservation, nine children are under the care of the father, an uncle and a grandfather, each a convicted sex offender, a federal official said. Two of the children, brothers who are 6 and 8, were recently observed engaging in public sex, residents said.

“Those little boys are crying out for help,” said a neighbor, who called the Bureau of Indian Affairs Police but said that officers declined to take a report or notify child welfare officials.

Another member of the tribe said that police officers and social workers failed to act after a 9-year-old girl described giving oral sex to a man.

Neither the tribe nor the federal government provided current figures on abuse, but in 2007 there were 26 confirmed cases of child sexual abuse and nearly 10 times as many allegations of abuse or neglect. McDonald said she presided over 20 to 30 cases of child sexual abuse each year. In 2011, fewer than a dozen cases of sex crimes against children were prosecuted by either the tribe or the federal government, which has jurisdiction, according to federal and tribal records.

Betty Jo Krenz, a former tribal social worker, said she oversaw 131 children — 100 more than the state’s average caseload. In some instances, members of the tribe say, there are generations of victims from the same family who have been preyed upon by generations of child rapists from other families. Others abuse their own children, including one tribal government employee who publicly complained that his young daughter had bitten his penis, according to a relative of the man and a federal official.

Federal agencies, however, have sought to minimize the extent of the problem, including disciplining employees who have spoken publicly about sexual abuse and questioning the competence of others, according to federal and tribal officials.

Thomas F. Sullivan, a director of the federal Administration for Children and Families, who has emerged as a crucial whistle-blower, is among those who have been prevented from speaking to reporters, he said. Still, his periodic reports to his superiors in Washington have been blistering.

“If we fail in our role as leaders, we will deserve the same condemnation society so correctly applied to those leaders at Penn State and in the Catholic Church who, knowing of the abuse being inflicted on children by their colleagues, did nothing, failing in their basic obligation to protect children,” Sullivan wrote last month to his supervisors.

And weeks before the scheduled federal takeover Oct. 1 of the reservation’s social service system, which is responsible for the care of the tribe’s sexually abused children, senior staff members at the Bureau of Indian Affairs continued to play down the issue.

Hankie Ortiz, deputy bureau director of the Office of Indian Services, said the media and whistle-blowers had exaggerated the problem.

“Their social service program has made steady progress,” Ortiz said, adding that she was unable to discuss specific cases under privacy laws or because she was unaware of them.

Roger Yankton, the tribe’s chairman, did not respond to requests for interviews.

But in a letter published last month in The Devils Lake Journal, a local newspaper, tribal officials cast blame on whistle-blowers and a lack of federal money.

“The tribe’s elected leaders and its people are well aware of the gravity and difficult nature of these problems,” the letter said, “particularly because we live with their consequences every day.”

But members of the tribe say their leadership has often sought to hide abuse.

McDonald said that the police investigated sex crimes against children only if a victim requested hospitalization, and that tribal leaders frequently sought to sway judges’ opinions improperly. She said she was forced to dismiss many cases because social workers forgot to submit required paperwork.

“The perpetrators know they can get away with it because the authorities don’t do anything,” said Joanne Streifel, a tribal elder.

Among the sex offenders is Quentin Yankton, 61, who stands 6-foot-5 and is a brother of the tribe’s chairman. He was first convicted of raping a child in 1976, state records show. In 1992, he was convicted of a similar crime after he forced his 15-year-old niece into sex. The girl became pregnant with twins, and DNA analysis showed that he was the father.

Yankton told the police, according to court documents, that he thought he was entitled to have sex with his niece because she told him that she had previously been sexually abused by her father.

Yankton was sentenced to 12 years in prison. The girl’s father was never prosecuted, but Alfred Longie, 67, a half-brother of the men, was convicted in 2008 for undressing and rubbing the genitals of a 12-year-old who had passed out after he had given her alcohol.

Joseph Alberts, 59, who plays Santa Claus for the tribe, was convicted of rape in 1983 and in 1986 was found guilty of committing lewd acts with a child under 14 on four occasions. He served one year in jail for that crime and 18 months for the rape.

In another case, after a woman tried to burn down her house with her 5-year-old daughter inside, the girl was put in a foster home where a sex offender was living, according to Sullivan and a member of the tribe. Once the foster parent’s criminal record was discovered, the tribe removed the child and put her back in her mother’s home.

But when the child proved too much for the mother to care for, Sullivan said, she sold her daughter back to the family of the registered sex offender for $50 and a ride to Grand Forks.

© 2012 The New York Times Company