A SCOTTISH grandmother has pled guilty in a United States court to killing her step-daughter, 37 years after the child's violent death.

Mary ''Rae'' Morgan, 58, one of four children from Ayr, married a US serviceman and emigrated to Illinois in 1960. She has admitted the manslaughter of four-year-old Michelle Ann, whose death occurred barely a year after Morgan's arrival in the US.

She had been accused of stamping repeatedly on the child's stomach, the climax of months of abuse and torture. Her secret had remained hidden for more than 35 years after the US Air Force and civilian authorities refused to pursue the child's killer.

Morgan was arrested and charged in Texas in December 1996, after Michelle's brother, George, 45, who is serving a 45-year sentence in Missouri for raping his own step-daughter, told police their stepmother regularly abused them. He was eight years old when his sister died.

He said his step-mother stamped on Michelle's stomach and held her head under water on the day before she died. US Air Force records showed the child had been treated for 20 separate injuries in the last year of her life at a military hospital in Illinois.

Morgan, who has four children and numerous grandchildren, could have faced death by lethal injection if found guilty of an original charge of first degree murder. However, earlier this month, her legal team plea-bargained for an involuntary manslaughter charge, with a maximum penalty of eight years in prison.

She is on bail and staying with relatives in Missouri, and it is expected she will be sentenced in December. She is under house arrest and wears an electronic surveillance tag on her ankle.

Morgan married former US Air Force policeman Billy Morgan, who was serving at Prestwick in 1960, and emigrated to Illinois later that year.

Mr George Morgan said yesterday: ''I'm glad she's finally admitted it. Michelle's memory can be laid to rest.''

His step-mother had claimed Michelle suffered broken bones and multiple bruising during numerous fainting episodes.

At one stage, doctors were so concerned they admitted the child to hospital for a month to monitor her for epilepsy. Michelle suffered no fits during her stay and, according to hospital staff, would scream whenever her step-mother came to visit - settling down after she left.

However, nobody took notice of the warning signs and on August 11, 1961, Morgan tortured Michelle for the last time.

Three years later, an internal Air Force inquiry concluded Michelle had been the victim of the then newly recognised ''battered child syndrome''.

Illinois State Police Special Agent Kurt Sachtleben, who led the investigation, said military and civilian authorities could not agree on who should investigate the case because of a dispute over whether it was a civilian or military matter.

The US Air Force had claimed that as the child was a civilian and the family home was off-base, it was a civil matter. The case was further complicated when Coroner Clifford Kane, who originally examined Michelle's death, did not release her death certificate until he retired in 1976, 15 years after the child died.

He gave the cause of death as ''possible viral pneumonia''. Prosecutors who exhumed the remains in December 1996 later confirmed she had been the victim of abuse.

Morgan could not be reached for comment yesterday but her lawyer, Mr Burton Shostak, said at his office in St Louis, Missouri: ''She decided to take the deal because it would be better for her to get this behind her and to take enormous pressure off her husband and other children.

''She is very sad that she lost a child. She is remorseful of the fact that it all happened and what it cost her other family members.''

Morgan, who made regular visits to her relatives in the UK, has been working as a missionary for the Christian Centre Assembly of God Church in West Columbia, Texas.

She and her husband, 66, a US citizen, were well known locally for their devotion to their family and their work with orphaned children in Mexico.

No-one from the US Air Force was available for comment yesterday.