A Prince George's County judge accused police of misconduct yesterday and threw out statements that he said police obtained illegally from nurse Jane F. Bolding, who is charged with murdering three hospital patients. Prosecutors called the action a "major blow" to their case.

Judge Joseph S. Casula, in a 53-page ruling, leveled harsh criticism at the three Prince George's County detectives who interrogated Bolding for 22 hours, saying that "the police misconduct was a purposeful and flagrant violation" of her constitutional rights.

After a three-month review of transcripts of courtroom testimony, Casula said that the detectives "illegally detained the defendant for investigatory purposes."

Bolding faces three charges of first-degree murder and seven counts of assault with intent to murder for allegedly administering massive doses of potassium to five patients from March 1984 to March 1985 at Prince George's Hospital Center.

Bolding was questioned by the three detectives for 22 hours and, according to court records, had had only four hours of sleep in the previous 48 hours when the questioning began on March 19, 1985.

In his ruling, Casula said prosecutors could not use a statement that Bolding gave police implicating her in the September 1984 death of Elinor Dickerson, 70, and in the death of a male patient she could not identify. During the police questioning, Bolding also wrote a letter of apology to Dickerson's family.

During courtroom testimony in October, Bolding said that she agreed to write the letter after hours of police questioning. For most of the 22 hours, Bolding said she had maintained her innocence as police accused her of injecting as many as 17 intensive care patients with lethal amounts of potassium. Bolding later testified that at the end, Detective Mike McQuillan began writing documents charging her.

"He said, 'Just tell me one name, and we can tear up the papers,' " Bolding told the court. "I was tired. My stomach was upset. I would fall asleep, and he would wake me up. He told me as soon as I was done writing the letter, he would bring me a cot in, and I could get some sleep. He said he was going to use the letter to help me."

Bolding, now 30, has said that during the questioning she was denied access to a lawyer. Detectives, however, said that Bolding did not want to talk with two lawyers who came to the police Criminal Investigations Division headquarters in Forestville while she was being interviewed.

Casula ruled that "the statements of the defendant were not sufficiently purged of the taint of the illegal detention and are therefore inadmissible at the trial."

The long questioning of Bolding has been the object of controversy since she was first charged in March 1985 with one count of first-degree murder, that of Dickerson. That charge was dismissed in May 1985 by then-State's Attorney Arthur A. (Bud) Marshall Jr., who cited a lack of evidence. Marshall also said Bolding's statement to police might not be admissible because it followed almost 24 hours of police questioning.

She was indicted by a grand jury in December 1986 after prosecutors received a report on the mortality rate at the hospital's intensive care unit prepared by the federal Centers for Disease Control. According to the report, a disproportionate number of Bolding's patients suffered cardiac arrests while in her care. She was the attending nurse in 57 cases -- or 40 percent -- of the 144 fatal and nonfatal cardiac arrests recorded at the hospital, then called Prince George's General, in a 14-month period.

"It is an understatement to say that the police version . . . flies in the face of reality," Casula said in the ruling released yesterday.

"In their zeal to elicit a statement from Bolding, the state and its agents substituted expediency for constitutional safeguards. There are simply no shortcuts around the Constitution," Casula wrote. "In those cases where the state and its agents attempt to employ such shortcuts, as they did in this case, their conduct must be condemned."

The ruling follows a request to suppress Bolding's statements filed in October by Bolding's attorney, Fred R. Joseph.

"We are all very excited. It was a hard-fought case," Joseph said yesterday. "We've been fighting this for nearly three years and I feel personally vindicated. And my client feels vindicated as well," he said.

Robert Harvey, chief of Criminal Trials Division in the county state's attorney's office, said yesterday that lawyers were "reviewing the opinion and are studying what our options will be. Until that is completed, we'll have no further comment."

Police declined to comment on Casula's ruling. Prosecutors can appeal Casula's ruling, or proceed with the trial, scheduled for May 9, or they could decide to drop the charges.

Bolding also is charged with killing Isadore Schreiber on Oct. 12, 1984, and Martha Moore on Oct. 28, 1984. The other charges involve alleged attempts to kill Mary Morbeto on March 9, 1984; Schreiber on Oct. 2 and Oct. 11, 1984; Moore on Oct. 28, 1984, and Gordon Dodson three times, on March 2, March 3, and March 6 in 1985.Staff writer Keith Harriston contributed to this report.