Ashley Snead, a 10-month-old Springfield girl who died of poisoning while in the care of her baby sitter, had been ingesting a prescription drug intended for older children or adults "maybe longer than two to three days," a toxicologist testified yesterday in a Fairfax County court.

Toxicologist Anh N. Huynh testified that on July 28, the day that Ashley died, she could have taken as many as nine tablets of the drug, imipramine, which is used to treat depression in adults and bed-wetting in children older than age 6.

Huynh's testimony came on the first day of Martha E. Guba's trial at Fairfax Circuit Court on a neglect charge. Guba, 58, was indicted on the felony charge in November in the death of Ashley, one of several children Guba cared for in her Springfield home. Guba pleaded not guilty to neglect charge. If convicted, she could be fined and sentenced to up to 10 years in prison.

In his opening statement yesterday, prosecutor Raymond Brownelle maintained that Guba had administered the drug to Ashley to keep her quiet. The prosecutor said that people remarked that "it was so quiet" at Guba's home at 6145 Bardu Ave., where she provided home day care service for up to eight children.

"This is not a one-time overdose of this drug," Assistant Commonwealth's Attorney Brownelle told the jury. "This is a chronic administering of that drug."

Guba's attorney, Thomas J. Morris, painted a picture for the jury of a "loving, concerned baby sitter" who would greet Jane Snead, Ashley's mother, at the door each morning with open arms.

According to homicide investigator Gary Healy, Guba, who is on a county list of day care providers, told police that Ashley had ingested what she believed to be an extra-strength Tylenol tablet before she stopped breathing.

Guba, who had been Ashley's baby sitter for about eight months, called Jane Snead at work and told her about the Tylenol, but reassured her that her only child was going to be fine, according to testimony at Guba's preliminary hearing. When Ashley stopped breathing, according to the testimony, Guba called back and said: "Get here fast, fast! Ashley's dying! Ashley's dying!"

Morris vigorously asserted his client's innocence of the neglect charge yesterday and said if Guba was guilty of anything it was "maybe of misjudgment" in not summoning rescue workers sooner. He said Guba had become concerned when she noticed Ashley begin to perspire and had turned up the air-conditioner and kept Snead posted.

Until toxicology tests were conducted, it was believed that sudden infant death syndrome had caused Ashley's death, Assistant Chief Medical Examiner Frances Field testified yesterday. She said the tests showed that Ashley died of imipramine poisoning.

Investigator Healy testified that when informed of the test results, Guba told him in a statement prior to her arrest that she had no idea how Ashley had come to ingest the drug. Healy said Guba explained that her husband had a prescription for the drug, but that she had thrown the drug out about a week before Ashley died. She later said she threw out the drug just prior to Ashley's death and found a tablet under her microwave oven, Healy said.

In the taped statement, which was played in court for the jury yesterday, Guba said the only thing she had ever administered to Ashley was brandy, which she rubbed on the child's gums to ease teething pain.

"I would never have given Ashley anything," she said tearfully. Pressed by Healy as to where the child got the imipramine, Guba replied: "I have no idea; I have no idea."

In testimony late in the day, Henry Horn, a doctor in Annandale, said he had prescribed the drug, and others, to Guba repeatedly in the last two years. At the prosecutor's request, Horn detailed Guba's contacts with him -- 13 alone in 1986.

In June 1986, Horn prescribed 30 tablets of imipramine after Guba said she was depressed because her husband had died of cancer, and the next month he gave her 100 more when the depression continued, Horn testified. Guba's husband is alive and attended the trial yesterday.

She was given another 100 the following August for nausea and vomiting, Horn testified, and more the next month when she told him she was upset because she saw her neighbor shoot himself. There were refills for other medicines after Guba told the doctor her house had been burglarized last January, and still others to help her cope with weight problems and the death of a grandchild, Horn said.

The trial, which is expected to last two to three days, will resume today in Judge Thomas J. Middleton's courtroom.