Defense lawyers will argue this week that months of complex scientific testimony in federal court here has failed to show that two Filipino nurses committed a bizarre series of murders and poisonings in 1975.

The defense moved to dismiss all charges immediately after federal prosecutors ended a nine-week struggle to convince a medically untrained jury that the nurses used a fast-acting paralyzing drug to murder two of their patients and poison nine others at the Veterans Administration Hospital in Ann Arbor, Mich.

The drug injections allegedly caused the hospitalized veterans to suffer sudden and medically surprising breathing failures during three hot weeks in July and August, 1975.

The sensational charges have produced a long, controversial and highly technical trial. Judge Philip Pratt, presiding over the trial in U.S. District Court here, has described it as "an extraordinary case for the federal judicial system." It is, in fact, virtually unprecedented in the federal courts.

The next move in the trial will come Tuesday when lawyers are scheduled to argue the defense motion to dismiss the charges against Filipina Narciso, 31, and Leonora Perez, 32, the accused nurses.

The presecution rested its case Wednesday after 41 days of testimony from 78 witnesses, most of them doctors, nurses, laboratory chemists and other medical personnel.

Two days later, defense lawyers filed the motion for a directed verdict of acquittal, contending that the prosecution's massive case had fallen short of the legal standard required to prove the nurses' guilt beyond a reasonable doubt.

Such motions are routinely filed at the end of the prosecution's case in criminal trials. They are rarely granted.

Narciso and Perez, who formerly worked as registered nurses in the VA hospital's intensive care ward, are accused of murdering two of their patients and poisoning seven others by rapidly injecting a paralyzing drug into the men's intravenous feeding apparatus.

The nurses, citizens of the Philippines who emigrated to this country six years ago, also are accused of conspiring to poison patients. The conspiracy charge alleges that two additional patients were attacked with drug injections.

The charges stem from an epidemic of more than 50 sudden breathing failures that struck 35 patients during the summer of 1975 at the VA hospital, a 400-bed federal facility serving acutely ill veterans from Michigan and parts of Ohio and Indiana.

Many of the hospitalized veterans suffered more than one breathing failure and were revived each time by doctors and nurses who provided artificial respiration. One man, William Loesch, a 26-year-old Vietnam veteran, mysteriously stopped breathing four times, testimony at the trial has shown.

Emergency resuscitation saved most of the patients, but there were 11 deaths associated with the breathing failures.

The prosection's case against Narciso and Perez is circumstantial and sometimes confusing prosecutors have acknowledged.

Assistant U.S. Attorney Richard Yanko, heading the prosecution, told the jury in opening arguments more than two months ago that there would be "no smoking-gun testimony." His case was consistent with that pledge.

There was no testimony that anyone saw the nurses inject a paralyzing drug into a patient. No witness claimed to have overheard the women plotting to poison patients.

The unique nature of the crimes charged forced and prosecution to present a substantial amount of obscure medical and scientific evidence to show that the breathing failures suffered by the patients, most of whom were seriously ill, did not result from natural causes.

The peculiar properties and effects of the drug allegedly used by the nurses emerged as a central issue in the prosecution's long case.

The drug is Pavulon, a compound containing a synthetic paralyzing agent, pancuronium bromide, that came into common use in American hospitals only a few years ago. The drug is quickly eliminated by the human body, a property that makes it difficult to trace.

Pavulon and similar drugs are used in surgery to paralyze the body's voluntary and semi-voluntary muscles, including the diaphragm and other muscles essential for breathing.

The drugs, known as "muscle relaxants," make it easier for a surgeon to cut through muscle tissue. But unless artificial respiration is constantly maintained, the drugs cause quick suffocation.

The prosecution attempted to link the accused nurses to the drug attacks by showing that one or the other was near each patient shortly before he suddenly stopped breathing.

Hospital personnel testified that Pavulon, which is not a controlled drug, was available in at least two unlocked refrigerators at the hospital during the summer of 1975.

The presecution presented hours of detailed testimony that probed each patient's medical history and attempted to educate the jury in the mechanics of breathing, the nature of intravenous medication and the precise effects of Pavulon.

The jury was forced to deal with terms like "neuro-muscular junction", the point at which nerves transmit the signals to muscles that allow movement and respiration, and "paroxysmal atrial tachycardia", a type of abnormally rapid heartbeat.

An FBI chemist testified that he made a five-month research effort to develop tests that could isolate and identify Pavulon in embalmed human tissues. Another chemist estimated in court that such an effort would have cost as much as $250,000 if conducted by a private laboratory.

Despite the massive scientific case, the defense was able to argue strongly in some cases that the breathing failures might have been caused by natural disease processes.

The trial is scheduled to resume Wednesday if the defense motion for a directed verdict is denied. The defense will then begin its case, which is expected to last two to three weeks and will involve still more scientific testimony.