A young Southeast Washington couple were found guilty of involuntary manslaughter yesterday in the death by starvation of their infant son.

A D.C. Superior Court jury of nine women and three men deliberated 90 minutes before returning the verdict against Tijuana Fauntroy, 22, and Leroy Johnson, 23, both of 600 Atlantic St. SE. They are the parents of Delonta Johnson, who died at the Atlantic Street address on Jan. 8, 1976.

Despite pleas from defense attorneys that the two be allowed to remain free on personal bond pending sentencing, Judge Nicholas S. Nunzio ordered that both be locked up immediately.

"I have never seen two people so emotionless before this court in a case concerning the death of one of their own children," Nunzio said.

He set sentencing for April 20. The maximum penalty is five-to-15 years in prison.

Miss Fauntroy testified that she thought she was giving the baby adequate care. Johnson declined to take the witness stand. Their attorneys argued that neither had any intention of harming the child.

The case was the first of its kind in D.C. Superior Court. Experts in the field testified that such cases are rare anywhere in the United States. It therefore presented some novel legal problems as well as what prosecution and defense attorneys agreed was a "human tragedy."

Dr. Leroy Riddick the deputy D.C. medical examiner, testified that he performed an autopsy on the body of Delonta Johnson on Jan. 9, 1976, and found that the child was 18 inches tall and weighed 5 ponds. He said records of the child's birth, on Nov. 8, 1975, showed that he had weighed 5 pounds, 3 ounces and had been 18 inches tall at that time.

Dr. Marh E. Robinson, a pediatric psychologist at Children's Hospital, testified that it appeared all the fat on the child's body and some muscle tissue had been consumed as a result of malnutrition. Other experts gave similar testimony.

Riddick testified with the assistace of colored slides of the baby's body. Photographs made from the slides were introduced over objections of defense attorneys Alan Rudd and Wallance Shipp that they were "highly inflammatory and prejudicial."

Miss Fauntroy testified that Delonta Johnson's birth had been two months premature and that he had been delivered by cesarean section. She said another of the two children of whom she and Johnson are the parents also was premature and had been slow to gain weight. She said she thought Delonta, too, was merely slow. Moreover, she said, the baby "spit up" much of its food.

The couple's other children have since been placed in the care of Johnson's parents. All are healthy, according to testimony.

The question for the jury to decide was whether the failure to provide adequate food and medical care for the baby - he was not taken to a doctor from the time he left the hospital after birth until his death - constituted "culpable negligence."

According to attorneys in the case, this is an unusual concept in the law. The general rule in criminal cases is that the prosecution must prove beyond a reasonable doubt that a defendant intended to commit the crime with which he is charged.

Prosecution and defense attorneys agreed that neither Miss Fauntroy nor Johnson had intended to starve the child to death. However, assistant U.S. Attorney Mark H. Tuohey III argued that D.C. law imposes on parents a duty to provide adequate food and shelter for their children. Judge Nunzio said in instructing the jury that he took this to mean that parents must provide health care as well.

The judge refused a defense request that the jury be instructed that they would have to find that the parents, intended to kill the child by starvation. Instead, he posed for the jury the "culpable negligence" question: whether the parents had failed "to exercise that degree of care rendered appropriate by the particular circumstances."