WASHINGTON (AP) _ The son of two former South Vietnamese diplomats, on trial for their murder, was calm and under control the morning he found his parents dead in their bedroom, the family's physician testified Wednesday.

''He struck me as controlled throughout the entire period,'' Dr. Philip James told a District of Columbia Superior Court jury hearing the prosecution's case against Tran Van Khiem.

Prosecutors presented medical evidence during the trial's second day to show that Tran Van Chuong, 88, and his wife, Nam Tran Chuong, 82, were murdered in the bedroom of their Washington home the morning of July 24, 1986.

Tran Van Chuong was ambassador to the United States and his wife was South Vietnam's observer to the United Nations during the Vietnamese War. The family was part of their nation's ruling hierarchy in the early 1960s, when one of their daughters, Madame Nhu, was married to the brother of then-President Ngo Dinh Diem.

A rift within the family dates back to the war period, when Madame Nhu became known as the ''Dragon Lady'' because of her support for Diem's brutal policies.

Assistant U.S. Attorney G. Paul Howes contends Khiem, 62, killed his parents in anger after they disinherited him in their wills.

Medical Examiner Dr. Carol McMahon testified Wednesday that she determined shortly after examining the bodies that they had been smothered and ''this was a double homicide.''

The wife was sprawled across her husband's body in a way that showed they died in an ''unnatural'' way, McMahon said.

James, the Chuongs' family doctor for several years, told jurors Khiem called the physician at his nearby office shortly after Khiem has said he and a family butler discovered his parents' bodies.

''He said, 'My parents are very old, my parents are very ill. They're in a coma,''' James said. ''He seemed calm. There was no great urgency or hysteria in his voice.''

The doctor said he came to the house immediately, examined the wife's body briefly and told Khiem, ''They're gone ... I said, 'I think they've been gone a long time.'''

Dr. James said he had seen Mrs. Chuong the day before her death and that she appeared healthy and did not have any of the scratches and bruises later found on her body.

The doctor said he immediately called police and that Khiem then called one of his sisters, Lecchi Oggeri.

That sister has said in police statements that her mother called her several times the night before the deaths and told her they were having an argument over Khiem's inheritance. However, a judge has not allowed prosecutors to present evidence on what Mrs. Oggeri said her mother told her.