Jean Harris, under the constant watch of a "suicide prevention" program at the Westchester County, N.Y., jail, spent her first full day in prison yesterday after declaring that she could not live "like an animal in a cage."

The convicted murderer of Scarsadale diet doctor Herman Tarnower refused to eat most of the prison food offered her during the first hours of her captivity, but did nibble on candy and cookies left with her Tuesday night by her lawyer, according to prison officials.

County Corrections Commissioners Albert Gray Jr. said he ordered Harris placed under the suicide prevention program's 24-hour monitoring after she told prison officials who admitted her to the facility Tuesday night:

"I can't see myself living like an animal in a cage for the rest of my life."

Harris, 57, the former headmistress of the exclusive Madeira School in McLean, Va., faces a mandatory prison term of 15 years to life for her conviction of second-degree murder in the shooting death of Tarnower, her lover of 14 years. Sentencing is scheduled for March 20.

Harris' lawyer, Joel Aurnou, plans to appeal the guilty verdict, but told reporters after the conviction, "I'm scared to death she won't live to see her appeal" made in the courts.

Gray, who was present when Harris was admitted to the 66-inmate all-women's section of the county jail, described her as "depressed, in a state of shock, disoriented."

"She was just overwhelmed, and didn't really seem to know where she was," he said.

Gray said Harris is staying in a 75-square-foot cell that is connected to a smaller "sitting room" with a television set. Under the suicide prevention program, around-the-clock shifts of "psychiatric aides" -- prison inmates who have been trained by the staff in suicide-prevention techniques -- are also on duty in the sitting room, Gray said. In addition, prison guards checks on Harris every 15 minutes, he said.

According to Gray, in her first day in the prison Harris expressed an interest in working in the prison library to one of the psychiatric aides stationed to watch over her.

Gray also denied reports that Harris was staging a "hunger strike" in an apparent attempt to starve herself to death, although he conceded that she was yet to eat her first prison meal.

He said yesterday she turned down a breakfast of cereal, French toast, bread and butter and coffee, but did accept a cup of tea. She also rejected the lunch menu of beef barley soup, egg salad on a roll, potato salad and chocolate pudding, but did not have two containers of milk, he said.

Gray said prison guards reported that Harris "has been eating her snacks" left by Aurnou and had ordered some tea bags from the prison commissary.

Yesterday morning Harris was interviewed for about 45 minutes by Dr. Edward Allen, the prison psychiatrist, and was also visited by her son and daughter-in-law.

Gray quoted Allen as saying Harris had been given medication, although the psychiatrist, citing the doctor-patient relationship, refused to confirm this.

Allen said that it was not unusual for new inmates to be placed under the watch of the suicide prevention program personnel, and that in some cases this had to be kept up for "weeks or months."

"We are just trying to make life more acceptable to her," he said of Harris. "We will try to give her all the support we can. . . . It is a very difficult case. Every person is different."