In the three years before he was shot to death by Jean Harris, Dr. Herman Tarnower prescribed for her 17 separate prescriptions for powerful and potentially addictive drugs.

They included, according to testimony in her murder trial here today, Valium, a sedative; Percadan, an extremely powerful pain-killer and Nembutal, a sleeping pill and anesthetic.

But the drugs provided to Harris most frequently by Tarnower -- in 10 of the prescriptions -- were amphetamines, the stimulant referred to, in the language of the street, as "speed." Harris, according to a local pharmacist who took the stand today, received three prescriptions for amphetamines from Tarnower in 1979, and earlier, testimony indicates that an unidentified prescription she received in the mail, the day after Tarnower was shot, contained amphetamines as well.

There was no testimony regarding the quantity of drugs prescribed to Harris in each prescription, or the dosage. There was also no testimony today regarding the effects of the drugs. But medical sources outside the courtroom noted that amphetamines, which have been traditionally used for weight control, are drugs which, used over a period of time, may result in irritability, hyperactivity, paranoia, and personality change. Medical experts also warn that the drug has the potential to be habit forming, as well. e

Former headmistress of the Madeira School in McLean, Va., Harris has been in court since October, charged with second-degree murder in the shooting death of Tarnower, her lover of 14 years. The defense, throughout, has called the shooting "accidental" and termed Harris "suicidally depressed." hIt has hinted, inside the courtroom, of the presence of drugs in this case, and outside the courtroom, mentioned drugs in stronger terms. It has suggested that Harris -- the anti-drug headmistress of Madeira -- might herself have been the victim of drugs, and that her supplier was none other than Tarnower.

"What's the one thing a dotor could give you that nobody else could?" a member of the defense team asked often, as the trial began.

It was a neat trick, presenting the accused assailant as victim and the victim as assailant, making the late cardiologist out to be an uncaring sort of Dr. Feelgood, dispensing drugs in place of love.

And today, with a White Plains pharmacist on the stand, the defense seemed to be setting the legal ground work to pursue that point. Having subpoenaed the pharmacist, Joseph Eisenberg, defense attorney Joel Aurnou asked him to identify his pharmaceutical records -- records that clearly indicated Harris' drug use and left no question that her supplier was Tarnower.

"And whose name was on the prescription?" asked Aurnou time and again, as he moved down a list of 17 prescriptions. "And who did you give it to?"

"Dr. Herman Tarnower," answered the pharmacist to the first question. "Jean Harris," he replied, to the next.

Under direct examination from the defense attorney, the pharmacist enumerated Harris' drug use, beginning with a 1977 prescription for methamphetamines, under the name Desoxyn, and ending with a prescription for the same drug in November 1979, four months before the doctor was shot. (There was testimony earlier in the trial that Harris, the day after the shooting, received in the mail a vial of pills having "a short name beginning with the letter D." That prescription was not included in the 17 prescriptions discussed today.)

According to the pharmacist, Harris received three prescriptions for methamphetamines in 1977. In 1978 she received four prescriptions for methamphetamines and a prescription for Nembutal, a sleeping pill; and Percobarb, a pain-killer. In 1979, there were three prescriptions for methamphetamines; Percadan, a pain-killer Plexodal, a barbiturte; and two prescriptions for Valiums. The seventeenth prescription was not identified.

The reaction of Harris, as the list of drugs was recited in court, was composed but tense. Pale, visibly irritable and exhausted, she said nothing as her attorney questioned the pharmacist. But later, when prosecutor George Bolen began questioning the witness, and suggested that someone might have forged the signatures, she was outraged.

"That's disgusting!" she snapped at her lawyer, in a voice that could be heard in the first two rows of the courtroom and possibly by the jury as well. "He knows what the signature is . . ."

Her lawyer had already objected. But a second attorney, a young woman, turned her attention to Harris in a soothing gesture that is seen more and more often at the defense table.

"SSssshhhhhh," she said.