A federal judge responded to nine weeks of prosecution efforts here by throwing out half of the major charges against two Filipino nurses on trial for murdering and poisoning their patients at a Veterans Administration hospital.

The nurses, Leonora Perez and Filipina Narciso, and their lawyers expressed joy and a sense of triumph after hearing Judge Philip Pratt's ruling in U.S. District Court. Federal prosecutors acknowledged that they were not happy, but maintained that their case is still "substantially intact," and said they remain confident of conviction on the remaining charges.

The ruling came in response to a defense motion, filed last week, asking the judge to declare the accused women not guilty of all charges that they used paralyzing drug injections in 1975 to murder and poison their intensive care unit patients at the hospital in Ann Arbor, Mich.

Such motions for a directed verdict of acquitfal are rarely granted.

Perez, 32, was completely cleared of murder charges by Pratt's ruling.Narcisco, 31, was cleared of one murder charge but still faces a charge of killing another patient. Both women must still face multiple poisoning charges.

The jurors will be informed of Pratt's decision Thursday when they return from a one-week recess and the trial continues into its tenth week.The defense will then begin to present its evidence and Narciso will be the first witness.

Pratt essentially ruled today that some 200 hours of testimony from 78, prosecutions witnesses during nine weeks of trial and failed to produce the kind of evidence on certain charges that would allow a reasonable juror to find the nurses guilty.

Pratt's broad ruling left unaltered only one of the 10 separate charges against the nurses.

The women each had been accused of murdering two patients and poisoning seven others by injecting Pavulon, a fast-acting paralyzing drug, into the men's intravenous feeding apparatus. The drug injections allegedly caused the men to suffer sudden and medically surprising breathing failures luring July and August, 1975.

The former VA hospital nurses also had been charged with conspiracy charge with conspiring to poison patients. The conspiracy charge had alleged that two additional patients - making a total of 11 - were given the potentially lethal drug injections.

Pratt today reduced the total number of patients involved in the case from 11 to eight.

He cleared Rerez of any involvement in the alleged murders, and declared her not guilty of four of the poisoning charges. She still faces three poisoning charges and conspiracy charge.

Pratt cleared Narciso of one murder charge and three poisoning charges. She still faces one charge of murder, four of poisoning and the conspiracy charge.

Despite the substantial reduction in the [WORD ILLEGIBLE] of charges against [WORD ILLEGIBLE] woman they still face the name [WORD ILLEGIBLE] minimum sentence - like in prison - if convicted by the jury on even one of the remaining poisoning charges.

The conspiracy charge carries a maximum penalty of five years in prison and a $10,000 fine.