A mistrial was declared tonight in the murder trial of former nurse Mary Rose Robaczynski, who was accused of killing a comatose patient by disconnecting his respirator.

Two jurors later said that the jury had been unable to decide if the patient was dead or alive when his life support system was unhooked. That, both prosecutors and defense had agreed, was the central issue in the case.

At the end, the jurors divided 10 to 2 in favor of acquittal, according to one member of the panel.

The jury had deliberated for a total of about 19 hours over two days when Criminal Court Judge Robert L. Karwacki ended the trial at 11:30 p.m. Five hours earlier, the judge had ordered jurors to continue deliberating, desipte their assertion that they were unable to reach a verdict.

Prosceutors said they would decide "as soon as possible" whether they would retry this case or any of three remaining murder charges against Robaczynski, who is accused of disconnecting the life-support systems of three other patents.

The 24-year-old Robaczynski remained as calm and sat as stick-straight when the mistrial was declared as she had during most of the 10-day murder trial.

She has broken down in sobs only once during the trial, when she took the stand in her own defense and testified that she did unplug the respirator of patient Harry Gessner, a Baltimore cab driver, but only because she believed he "had died" moments before.

She testified that his blood pressure was gone and his pulse "had disappeared" while she was taking it at about 5 a.m. on March 8, 1978.

The prosecution had maintained that the 48-year-old Gessner, although gravely ill, was alive at 5 a.m. and that Robaczynski had cut off his oxygen supply and killed him.

The defense contended that the patient was legally dead under Maryland law when the respirator was unhooked, and that, therefore, Robaczynski could not be charged with murder.

The jury was faced with a complex array of medical testimony bolstering each side's contentions in the case, and according to jurors who spoke tonight with reporters, the evidence was too "confusing."

"I think the most important thing is that people didn't know anything about medicine," said juror Clee Anderson Jr., 24. Anderson said the jurors were "confused" by the medical testimony.

Jury foreman Beverly Skotarski, 22, one of those holding out for acquittal, said, "When there is so much doubt, you can't convict someone, and we couldn't even decide whether he (Gessner) was dead."

Anderson agreed and added that the Maryland law giving the legal definition of death also had been confusing to the jurors.

The defense had hinged its case on the 1972 law that states, in part, that death may be legally declared when "spontaneous brain function" is absent.

Juror Robert David Jr., a machine operator, said he did not believe Robaczynski "intended to kill," and that this was an important consideration among the jurors.

During the trial, Robaczynski also admitted to unhooking the respirators of two other unconscious patients in her care at Maryland General Hospital. She denied that she had disconnected the life-support system of a fourth patient, whom prosecutors have charged she also murdered.