A Rockville babysitter went on trial in Montgomery County yesterday in the death of a 3-year-old girl who prosecutors said was "trapped" in the babysitter's "house of horrors" while her impoverished parents worked 14-hour days to get by.

Sandra Villacis, 32, baby-sat for Hilda "Frenese" Martinez from 7:30 a.m. to 9 p.m. five days a week and abused her for months before violently shaking the child and striking her head repeatedly against a hard surface in September 1998, Deputy State's Attorney Katherine Winfree told jurors in her opening statement.

"Being a child isn't supposed to hurt," Winfree told jurors. "But for Hilda Frenese Martinez, life became a waking nightmare."

Listening to a Spanish interpreter via a small earpiece, Villacis, who is from Ecuador, looked straight ahead and occasionally dabbed her nose with a tissue as Winfree told jurors that Villacis had lied for months about the bruises and scratches that Frenese's parents noticed on her legs, back, buttocks, neck and face. Villacis told the parents, who are from Honduras, that their daughter fell down in the park and in the bathtub and while playing in her home, Winfree said.

But an autopsy, performed after doctors had already removed part of the child's skull and brain to relieve the fatal swelling, found bleeding in the child's eyes and blood clots beneath a layer covering her brain--clear signs of a violent and fatal shaking, Winfree said.

"This was not an accident," Winfree told jurors repeatedly. "This was child abuse. This was murder."

Villacis, of the 5200 block of Crossfield Court, is charged with second-degree murder, involuntary manslaughter, child abuse and child abuse resulting in death. The most serious charge, second-degree murder, carries a maximum penalty of 30 years in prison.

But defense attorney William Brennan told jurors that the babysitter told the truth when she told police that Frenese had been running in her home during a game of hide-and-seek or tag and had tripped and hit her head against a doorjamb.

Although Winfree portrayed the child's mother and stepfather, Julia Carpio and Selvin Banegas, as working "from before sunrise until after sunset" to make a better life for Frenese, Brennan said they were "too busy and didn't care about this little girl."

Brennan said the child's stepfather had told police that her mother would "spank her" sometimes as punishment. Some injuries to the child might have occurred after Villacis "panicked" and shook the child to try to revive her after she fell and hit her head, the defense attorney said.

"She spent time with a little girl whose parents never spent time with her," Brennan said.

Although Brennan said prosecutors have no witnesses to testify that Villacis mistreated the child, Winfree said jurors will hear from a doctor about the state's best eyewitness: Frenese herself.

When the girl's parents took her to see a Silver Spring doctor about her bruises, cuts and nightmares, the doctor asked the child how she got a 10-inch-long, two-inch-wide bruise on her thigh, Winfree said.

The child, Winfree said, gave her answer in Spanish, which translated to "Sandra hit me with a doll."

CAPTION: Hilda "Frenese" Martinez died in 1998 after she was shaken and her head was struck, authorities said. She spent 13 1/2 hours a day with the sitter.

CAPTION: The attorney for Sandra Villacis said Frenese died after she hit her head on a doorjamb while playing.