Miriam Jesela Mejia, a native of the Dominican Republic who came to the United States last year on a diplomatic visa, was a frequent guest in the Alexandria apartment of her distant cousin Gladys Lizardo Venor.

"She always use to play with my little girl," Venzor said of her cousin. Sometimes she would sit and teach her how to write . . . my little girl really loved that."

Last Friday, something went wrong.

Mejia was arrested four blocks from the Venzors' apartment building by Alexandria police, who minutes earlier had discovered the body of 3-year-old Cynthia Venzor in an empty storage bin in the basement of the Creastview Apartments, where her parents live.

An autopsy report said Cynthia died of 82 stab wounds.

Yesterday, after Mejia had been arraigned in Alexandria's General District Court where she was charged with murder and ordered held without bond, police said they were baffled by the case.

"We have no motive whatsoever," said one detective familiar with the investigation. "We talked to her [mejia] through an interpreter and she gave no reason. She said the child hadn't done anything to her and the family hadn't done anything."

Police on Friday said they found a small kitchen knife that apparently had been used to inflict the wounds on the girl's face, neck, arms and hands. They also found Mejia about four blocks from the apartment complex near Landmark Shopping Center "just walking on down the road."

Last week police said Mejia had been living with the Venzor family for a few days. But yesterday Hustiono Venzor, the father of the slain girl and a construction worker, said Mejia had never lived there.

Mrs. Venzor, whose sister is married to a half brother of Mejia, said she and her husband were both at work Friday when Mejia came by to visit their daughter. She was being cared for by the victim's grandmother, who lives with the venzors.

The Venzors could not say where Mejia was living or employed. Police and immigration authorities said last night they were also unable to provide that information.

One immigration official did say that Mejia had entered the United States on Oct. 24, 1979, on a G-5 diplomatic visa.

"The G-5 is the lowest level diplomatic visa," said the immigration official."It is normally for a servant or domestic help for an international organization or the home of a diplomat. Almost every diplomatic household in the city has one. Just like a washer and dryer, they're a status symbol."

Cynthia Venzor was an only child who, unlike her parents, was rapidly learning English. Her death stunned residents of the Crestview Apartments complex, particularly the Venzors' neibhbors at 324 S. Whiting St.

"That was the prettist little child you've ever seen," said one neighbor who said she was shaken by the slaying. "She had jet black hair down to her waist. Everybody in the area that saw her loved her."

Yesterday the Venzors visited with friends in the District and tried to add at least some understanding to their misery. "She [mejia] was always normal around my little girl," said Gladys Venzor. "You would never have thought anything was wrong."

The funeral will be held today at Sacred Heart Catholic Church in the District.