A Montgomery County jury convicted a Rockville babysitter yesterday of repeatedly abusing a 3-year-old girl in her care and finally killing the child by violently shaking her and causing fatal brain injuries.

Sandra Villacis, who had testified that the child accidentally hit her head on a door frame during a game of tag, closed her eyes as the foreman announced that the jury hadn't believed her. "Guilty," the foreman said, to charges of involuntary manslaughter, child abuse leading to death, and nonfatal child abuse.

Villacis, 32, faces up to 45 years in prison when she is sentenced March 22 for the death of Hilda "Frenese" Martinez in September 1998. After a six-day trial and seven hours of deliberations, the jury acquitted the babysitter of a second-degree murder charge.

One of her lawyers, William Brennan, said Villacis also could face deportation to her native Ecuador. Though Deputy Montgomery State's Attorney Katherine Winfree asked the judge to detain Villacis as a flight risk until her sentencing, Montgomery Circuit Court Judge Paul H. Weinstein released Villacis on her current $50,000 bond and ordered her to surrender her passport.

"She's not a danger to anybody," Weinstein said, adding that before sentencing, Villacis must arrange for her two young daughters, including one who is autistic.

Montgomery County prosecutors argued that Villacis had targeted Frenese and abused her for months, leaving scrapes and bruises on her arms, legs, neck, head, ear and eye. On Sept. 15, 1998, during a fit of rage over the little girl running through her immaculate home, prosecutors said, Villacis shook Frenese on the ground so hard that her head snapped back and forth and struck the floor, bursting blood vessels in her eyes and brain and causing fatal brain swelling.

Frenese, whose Honduran parents worked 15 hours a day cleaning apartments, was in Villacis's care at least five days a week from 7 a.m. to 9 p.m., prosecutors said.

One month before Frenese died, prosecutors said, her parents took her to a Silver Spring pediatrician for bruises, insomnia and nightmares. When the doctor asked Frenese how she got a 10-inch-long, 2-inch-wide bruise covering her upper thigh, the girl said in Spanish, "Sandra hit me with a doll."

"Look at the damage, the brutality inflicted on this small, helpless child's body," Assistant State's Attorney Alex Foster told jurors in closing arguments as he pointed to pictures of bruises covering the child's buttocks.

But when she took the stand Tuesday in her own defense, Villacis sobbed and repeatedly denied killing the child. She said she and her own daughter, Iliana, who was 6 at the time, were running with Frenese down a hallway while playing tag before she realized Frenese had fallen and hit her head on the bathroom door frame.

"I just picked her up and called her by her name over and over again," Villacis sobbed, as she knelt on the courtroom floor and demonstrated how she had tried to revive the child by shaking her.

Speaking through a Spanish interpreter, Villacis said she was "desperate" and "anguished" and shook the child "many times" because, "I only wanted her to react. I never meant to do her any harm."

Villacis said the long bruise on the child's leg and red fingerprint marks on her arm happened when she tried to keep Frenese from falling as she got out of the bathtub. Other bumps and bruises, Villacis said, happened when Frenese fell in the park, toppled over in a chair and bumped her head while playing.

Brennan said he was "disappointed but not surprised" by the jury's verdict, based on the weight of the prosecution's medical evidence.

Four doctors testified that the little girl's head injuries were so massive that they could not be attributed to a small child's clumsiness or a fall during a game of tag.

Jonathan Arden, the District's chief medical examiner, testified that the extensive bleeding on Frenese's brain and in her eyes were telltale signs of shaken baby syndrome. "This is far outside the realm of tripping and falling or child's play," Arden said.

CAPTION: Sandra Villacis, convicted of child abuse, involuntary manslaughter.