Baltimore City prosecutors decided yesterday that Maryland's law defining death is too ambiguous for them to win a murder conviction against a former nurse who admitted unhooking the respirators of three patients.

As a result, knowledgeable sources said, all the murder charges pending against 24-year-old Mary Rose Robaczynski will be dropped.

Robaczynski's first murder trial ended in a mistrial last week after the jurors found themselves unable to agree whether the patient Robaczynski allegedly killed already was dead at the time she unhooked his respirator.

While the Robaczynski case may prompt changes in the 1972 Maryland statute defining brain death, experts said yesterday that the circumstances of this case were so unusual that it will have little impact on the continuing national debate on the definition of death.

Prosecutors and defense attorneys, who met yesterday to discuss the decision, said they had no comment on the case.

Baltimore City State's Attorney William A Swisher plans to recommend that the legislature amend the statute to avoid future confusion, sources said yesterday.

Brain specialist Francis C. Mayle, head of the Maryland medcial society, said his group also may see if it is possible to improve the law, which it supported in 1972.

That statute states in part that a patient may be declared legally dead when there is an absence of "spontaneous brain function." The defense build its case on those three words, maintaining that 48-year-old Harry Gessner was "brain dead" before the disconnection.

One juror said that each of her fellow jurors put his or her own interpretation on the word "spontaneous" and that this led to the 10-to-2 deadlock that forced the judge to declare a mistrial.

Some legal and medical experts now believe that the world "spontaneous" should be left out of future statutes because of the potential confussion.

Eighteen states, including Maryland and Virginia have statutes that establish a standard for brian death, according to University of Pennsylvania law professon Alexander Capron, who has drafted some of the laws. Many of those include the word " spontaneous."

The 32 other states and the District of Columbia still define death as the cessation of all bodily function, including breathing. Under these laws, a patient who is being maintained on a respirator would be considered legally alive even if there were a total cessation of brain activity, Capron said.

The head of Concern for the Dying, a national group advocating the right of a terminally ill patient to refuse treatment, said yesterday he fears the prosecutors' decision in the Robaczynski case might be interpreted by some patients' life support systems.

"There is a tremendous danger here for a third party to take upon himself this kind of decision," A. J. Levinson said yesterday.

At the Robaczynski trial doctors testified that no nurse has the right to disconnect a respirator and that such a disconnection would go against standard medical procedure.

Robaczynsi resigned from her joob at Maryland General Hospital after she was accused of disconnecting some patient respirators. She still faces a license revocation hearing before the Maryland Board of Nurses Examiners.

Her attorneys, Joseph Murphy and George Helinski, however, said she has given them ther nursing license, a letter of resignation from the profession and a pormise that she would never again attempt to practice anywhere.

Robaczynski, who took the witness stand at her trial, admitted to disconnecting the respirators of three patients, who she believed already were dead. She denied the disconnection of a fourth patient, whom prosecutors charged she also murdered.