The Maryland state medical examiner's office has ruled that the death of a 13-month-old Rockville girl who allegedly was sexually assaulted by her babysitter was a homicide, officials said yesterday.

The babysitter, Timothy Conrad Phillips, 30, is being investigated in connection with the death of Amani Renee Robinson and is being held in lieu of $250,000 bail on charges of child abuse and second-degree sex offense.

Phillips also is being investigated in connection with the 1997 death of Andre Michael Whitworth, a 2-year-old boy whose mother found him badly beaten and unconscious shortly after Phillips baby-sat for him, authorities said. Whitworth's Jan. 31, 1997, death was ruled a homicide.

Montgomery County State's Attorney Douglas F. Gansler confirmed yesterday that an autopsy conducted by the medical examiner found evidence of homicide. He said he would not file charges until he saw the medical examiner's final report, but called the girl's death a "heinous crime."

"A 13-month-old child is not seriously sexually abused at the level this child was and just coincidentally dies of natural causes," he said.

According to authorities, Phillips had offered to watch the child on Aug. 27 at her Rockville home while her mother was at work, then called 911 to report that a child had drowned in the bathtub.

When paramedics arrived at the home in the 100 block of Moore Drive, they said they found the little girl lying on the living room floor. Authorities said neither she nor the bathtub was wet and her lungs contained no water.

The girl was taken by ambulance to Shady Grove Adventist Hospital, where she was pronounced dead shortly after 9 a.m., officials said.

A Montgomery County detective who arrived at the hospital's emergency room said he found cuts and tears around the girl's anus, and hospital officials said the injuries appeared to be the result of sexual abuse, according to court documents.

The girl's mother, Amy Hogan, told police she hadn't notice any injuries when she changed her daughter's diaper earlier that morning, according to court documents.