VIENNA, Austria (AP) _ An Austrian newspaper reported today that one of the four assistant nurses who confessed to killing patients at a Vienna hospital may have slain up to 200 over the past six years.

Police refused comment on the report, which was unattributed. Police officials declined to give any new details of the grisly crime as a news blackout imposed by Vienna police chief Guenter Boegl took effect.

Boegl has threatened legal action against police if they leak details of the investigation to the media, the tabloid Neue Kronen Zeitung reported.

Also today, Chilean-born assistant nurse Dorah Eugenie Ferrada-Avendano, who reportedly informed a doctor about the killings at Vienna's Lainz hospital, was freed after two days of questioning, Hubert Brem, a spokesman for state prosecutors, said.

The four assistant nurses, who reportedly confessed to killing a total of 49 elderly patients with overdoses of medicine or by forcing water into their lungs, claim they engaged in ''mercy killings.'' But police said the methods they used made that motive unlikely.

The Neue Arbeiterzeitung, the daily paper of the Socialist Party, reported that Irene Leidolf, one of the four assistant nurses, accused her colleague, Waltraud Wagner, of killing up to 200 people. Ms. Leidorf was said to have insisted in interrogations that her figure was not exaggerated.

Brem said, however, that Ms. Wagner, 30, has retracted some of her initial confession to police. Police have said Ms. Wagner confessed to 39 killings. Brem declined to specify exactly how she has changed her initial statement, which her lawyer Wilhelm Philipp referred to as a ''so-called confession'' that would not suffice for a murder conviction.

Senior police investigator Max Edelbacher has said the number of victims at the hospital could be higher than the 49 killings admitted by Ms. Wagner, Ms. Leidorf and their colleagues Stephanie Mayer, 50, and Maria Gruber, 25.

On Wednesday, the director of the hosptial department where the killings occurred was suspended after being accused of failing to cooperate fully with police when they investigated earlier reports of killings at the hospital.

The doctor, Franz Pesendorfer, consistently has defended his role in the investigation and the conduct of officials in his department at the Lainz hospital, Vienna's fourth largest.

The case has prompted a nationwide debate into the overtaxed Austrian health care system. A nationwide television discussion Wednesday night focused on the strains placed on hospital personnel.

Psychologists are being sent to the Lainz hospital and other Vienna hospitals to reassure patients and staff, psychiatrist Stefan Rudas said.

Police and health officials have raised doubts about amassing evidence to convict the women, who have not yet been charged, in any eventual court case.

City authorities on Wednesday sanctioned the exhumation of an undisclosed number of bodies of presumed victims.

But Dr. Wolfgang Enenkel, a heart specialist appointed to replace Pesendorfer temporarily, said today he doubted a tranquilizer said to have caused some deaths could be detected in sufficient quantity to prove murder.

Many old people take the tranquilizer, he said.