Prosecutors began their attack on the credibility of Jean Harris at her murder trial today, challenging her story that she "never intended to harm" Herman Tarnower and that she struggled with her lover for the gun because she "needed to die."

They questioned her on her depressions and drug dependence. They questioned her on her alleged ignorance of handguns.

But despite her somewhat drawn appearance -- and a mouthed stage whisper to her attorney at the end of the day that she "couldn't bear it" -- Jean Harris defended herself well. She kept her composure. She abstained, most of the time, from her notorious sharp-edged remarks. And, no matter what a prosecutor asked her, she found a way to say what she wanted to say.

Hadn't the salesman in the gun shop explained to her how to remove a spent cartridge, prosecutor George Bolen asked her.

"He could have," said Harris dryly, "but I wasn't listening . . . I wasn't planning to worry about how to get the spent cartridge out."

Hadn't the salesman in the gun shop explained both the loading and unloading of a pistol, the prosecutor pressed.

"Mr. Bolen, he may have explained everything there was to know about a handgun," began the defendant, "but I had only one purpose in buying that gun and that was killing myself . . . I just wanted to fill it with a bullet and shoot myself . . . I didn't listen to anything else he told me. I didn't ask him anything else. The only thing I asked him was 'How do you put a bullet in the gun?"

Former headmistress of the Madeira School in McLean, Va., Harris has been in court since October, charged with second-degree murder in the shooting of her lover, Dr. Tarnower, in the bedroom of his home. The prosecution, noting that the doctor had been seeing a woman 20 years Harris' junior -- Tarnower's assistant, Lynne Tryforos -- claims Harris shot the doctor intentionally, in a jealous rage. Harris herself says she drove to her lover's home for "one more moment of peace" before she committed suicide.

Today, her fourth day on the stand, she voiced those feelings again in the morning as the defense finished its direct examination, and in the afternoon, as the prosecution began its cross-examination. Dressed in a bright blue silk blouse and cream suit, a triple strand of pearls at her throat, she was more composed than she had been in the past few days. She was calm as she told her lawyer, Joel Aurnou, that yes, she was still taking medication. (The prosecutor had that stricken from the record, but the jury had already heard.) She was also composed as she answered the first in a series of devil's advocate questions.

"Why did you want to die at Purchase, New York?" the defense lawyer asked.

"Hi [Dr. Tarnower] and I talked about that . . . we talked about how we both loved the pond, we'd both been on it a hundred times and he wanted to die there . . . and I wanted to die there, too . . . ," said Harris, tiredly.

"Where did you feel your home was?" asked Aurnou.

"Where Hi was was home to me . . . I'd been welcomed there for 14 years, with 'Welcome home, darling,' and that was home to me . . . Certainly, Madeira wasn't home," she said.

"What was in your mind when you struggled for the gun?" asked Aurnou.

"What I've said," said Harris, "I wanted to get the gun . . . I needed to die . . . everything Hi did and said made it more necessary . . ."

Why did she try to shoot herself in the doctor's bedroom, asked the lawyer, why didn't she go to the pond as she had planned?

"I meant to," said Harris, "I got my pocketbook and went to walk out, but when I felt the gun, I took it out to use it there . . . There was a point it was important for Hi not to know I was going to commit suicide, I just wanted to have a few more minutes of pleasure with him . . ."

"I have lived a quiet private life and I wanted to die a quiet private death . . . It wasn't meant to be a grandstand play, though it certainly looks that way now . . ."

Aurnou asked his final tough question, the one the jurors have probably wondered about.

"If you felt so strongly about dying then, why haven't you done anything to kill yourself since?" he asked.

An objection from the prosecution prevented the reply.

The assistant district attorney, Bolen, began his cross-examination of Harris by concentrating on her depression and drug dependence. But despite Harris' admission that she had taken "medication" since since 1971, when she was a headmistress at the Thomas School in Connecticut, the prosecutor was unable to get an admission from Harris that she had asked the doctor for drugs.

"Did you ask him for help?" asked Bolen.

"After talking with Hi for 10 minutes I didn't feel anything bad about anything anymore," said Harris, parrying nicely.

At another point in his cross-examination, Bolen asked Harris about the layout of the doctor's bedroom, and her proximity to the spiral staircase that would have taken her out of the house.

"Couldn't you have walked down the spiral staircase?" he asked.

"I certainly could have," said Harris, "and I wish I had."

There were no tears as she was cross-examined, in fact, she shed very few tears today in contrast to her breakdowns earlier this week. But Harris did cry once today, when her attorney asked her to describe her feelings at the police station when she was told that Tarnower had died.

She stared at the ceiling, she looked quickly at the floor -- anywhere but the jury and the room filled with spectators -- her face turned red and she began to cry.

"I had asked them to please see if I could get to see Hi at the hospital . . . then somebody came and said to me, 'Oh, he passed on' . . ."

She struggled for her voice, crying. "One of the lawyers was with me, I took hold of him . . ."

"What a dumb expression," she said, "'passing on' . . ."