The Philadelphia district attorney’s office on Tuesday challenged a claim by lawyers for a convicted Roman Catholic monsignor that prosecutors had persuaded another priest, now defrocked, to falsely admit to sexually abusing a 10-year-old boy in order to obtain the conviction. Lawyers for Msgr. William J. Lynn, a former senior official in the Archdiocese of Philadelphia who was convicted in June of child endangerment, filed a motion Monday in Pennsylvania Superior Court claiming that Edward V. Avery, the former priest, had not in fact abused the boy but had been pressured by prosecutors into signing a plea deal saying he had done so, in return for a lighter prison sentence than he might otherwise have received.
Monsignor Lynn was found guilty of endangering children by failing to stop abuse by priests under his supervision. He is the most senior official of the Roman Catholic Church in the United States to be convicted of charges relating to sexual abuse of children by priests.
The conviction was for lax oversight of Mr. Avery, who spent six months in a church psychiatric center in 1993 after an abuse episode.
Doctors said he should be kept away from children. But Monsignor Lynn sent him to live in a rectory and did not warn parish officials.
Mr. Avery’s alleged abuse of the boy was central to the conviction of Monsignor Lynn, whose lawyers are asking the court to reconsider its previous denial of bail.
The lawyers said in the motion that they received evidence in late August that Mr. Avery denied assaulting the boy, or even knowing him, and that he had passed a polygraph exam testing whether he was lying about the abuse.
In their motion, they said that prosecutors had refused to accept Mr. Avery’s offer to plead guilty to assaulting another boy and that they would only accept a plea that included admission of a conspiracy with Monsignor Lynn.
“It doesn’t do the commonwealth any good to get Edward Avery to plead on something other than conspiracy with Lynn,” Thomas Bergstrom, a lawyer for Monsignor Lynn, said in an interview.
But Hugh Burns, chief of the appeals unit in the Philadelphia district attorney’s office, said Mr. Avery had freely pleaded guilty to abusing the boy, as shown by his own testimony during his sentencing.
Mr. Burns also rejected the defense claim that prosecutors had “compelling reasons” to doubt the plea’s veracity.
“That’s just false,” Mr. Burns wrote in an e-mail. “Avery swore under oath that he was guilty, and as far as the record shows, he decided to plead because he knew what the evidence would show and how the jury would react to it.”
Monsignor Lynn is serving three to six years in a Pennsylvania prison.
Results of the polygraph test, according to the motion, were provided to the district attorney’s office by Mr. Avery’s lawyer, John P. Donohue.
But the filing said prosecutors failed to share that information with Monsignor Lynn’s defense.
“This newly discovered information leads to the disconcerting conclusion that the commonwealth was driven by a zealous and single-minded desire to try Appellant and obtain a conviction despite information that put into question the justice of pursuing that outcome,” the document said.
Mr. Bergstrom said the allegations are based solely on a conversation he had with Mr. Donohue in late August; that he had not seen the results of the polygraph test, and could not provide any documentation to verify the claims.
Mr. Donohue declined to comment because a judge imposed a ban on lawyers talking to journalists ahead of the trial of Charles Engelhardt, another priest, at which Mr. Avery is expected to testify.
The Archdiocese of Philadelphia is still conducting an internal investigation into abuse allegations against 11 of 26 priests placed on administrative leave after a scathing 2011 grand jury report charging it had spent years covering up reports of abuse.
On Tuesday, lawyers for nine people who say they were abused by priests filed a total of eight civil suits against the Archdiocese of Philadelphia, Archbishop Charles J. Chaput, former cardinal, Justin Rigali, and Monsignor Lynn, according to Marci Hamilton, one of the lawyers representing the plaintiffs.
The suits also name seven priests.
They bring to 18 the total number of civil suits filed in Philadelphia by those who have accused clergy members of sexual abuse, Ms. Hamilton said.