Former nurse Mary Rose Robaczynski, on trial here for murder, took the stand in her own defense today and tearfully testified that she disconnected the respirator of a comatose patient in her care because she believed he "had died" moments before.

The nurse, charged with murdering patient Harry Gessner by unhooking his life-support system also admitted disconnecting the respirators of two other unconscious patients in her care at Maryland General Hospital here. Prosectutors also have charged her with separate counts of murder in these cases.

The case went to the jury tonight, and jurors spent five hours deliberating before being sequestered for the night. Deliberations will resume Tuesday morning.

Earlier today, Robaczynski had testified that Gessner and the two other patients had no pulse and no blood pressure moments before she unhooked their life-support systems.

Baltimore city prosecutors however, have charged that when Robaczynski disconnected Gessner's respirator shortly after 5 a.m. on March 8, 1978, she killed him.

She also is charged with a fourth murder by respirator disconnection, but, in a clear calm voice today, she denied unhooking that patient's respirator.

Moments before Robaczynski had broken into sobs as she told of entering Gessner's room at 5 a.m., noting that his heart "was having changes," finding that his blood pressure could not be "heard or felt," and discovering that his pulse "had disappeared."

"Did you disconnect Mr. Gessner?" defense attorney George Helinski asked her.

"Yes," she said softly, "after I felt he had no pulse and no blood pressure."

Robaczynski, tears streaming down her face, said that in the seconds before the disconnection she had stood in Gessner's room. "I felt helpless," she testified. "I didn't know what to do."

During the trial, doctors have testified that no nurse has the right to disconnect a respirator under hospital procedures and that such a disconnection would go against standard medical practice.

On cross-examination, Assistant State's Attorney Howard Gersh asked Robaczynski why she did it.

"This patient had died while I was standing there and I could not do anything for him," the slim, dark-haired woman told the prosecutor. "And it was upsetting to me. I witnessed his death."

Pressed later on "what was the rush" to disconnect a deed man, Robaczynski said. "I was trying to act in the best interest of the patient. I felt helpless. I don't exactly know why I did it."

Robaczynski then repeated that she "felt the patient was dying and that he did die, yes."

Asked by Gersh if there is a difference between "dying and being dead," she said, "I would not do anything to hurt anybody."

Robaczynski's testimony was the last for the defense, whose case has hinged on Maryland's legal definition of health. The 1972 law provides, in part, that death may be legally declared by a doctor if "spontaneous brain function is absent."

A brain specialist, testifying for the defense last week stated that Gessner lacked "spontaneous brain function" while in the hospital's special care unit, but the prosecution yesterday, in its closing arguments, dismissed the doctor's testimony as too complex to understand.

Instead, prosecutor Gersh pointed to testimony by the same witness that he would not have disconnected the respirator himself.

The prosecutor contended that he had shown that Robaczynski had disconnected the respirators of eight different patients, including Gessner. Four of the patients died as a result of her actions, the prosecutor charged.

Gersh also contended that she "had no right" to do it and that Robaczynski's actions, in Gessner's case either "caused, contributed to or accelerated" the patient's death.

In his closing argument, defense attorney Joseph Murphy Jr. denied that his client was involved in eight disconnections.

He said that the defense, with its witnesses had placed a "reasonable doubt" in the jurors' minds as to what caused Gessner's death, and he stated that the defense admits "that respirator disconnection is wrong."

"However," he told the jury, "respirator disconnect is not murder."