By Dave Warner

PHILADELPHIA (Reuters) - Defense lawyers for the highest ranking church official to go on trial in the Catholic church's pedophilia scandal, charged with child endangerment, asked a judge on Friday to pick a new jury because a co-defendant pled guilty.

Opening arguments in the trial of Monsignor William Lynn, 61, former secretary of the clergy under the late Cardinal Anthony Bevilacqua, were slated to begin on Monday. A jury has already been selected.

Lynn was to go to trial with defrocked priest Edward Avery and Rev. James Brennan, who are among four others charged in the child sex abuse case that rocked the Philadelphia Archdiocese.

But Avery, 69, pleaded guilty on Thursday and was immediately sentenced to 2-1/2 to 5 years in prison on charges of involuntary deviate sexual intercourse and criminal conspiracy to endanger the welfare of children. He was accused of sex abuse involving a then 10-year-old altar boy.

Lawyers for Lynn, 61, who is charged with endangering the welfare of children and conspiracy, moved on Friday to delay the trial, asking for a new jury.

Referring to Avery's guilty plea and the news coverage surrounding it, Lynn's attorney Jeffrey Lindy told Common Pleas Judge M. Teresa Sarmina that a new jury was needed.

"We're not unhappy with the jury we got," Lindy told the judge. "But because of what happened yesterday, we don't see any way around it."

Prosecutor Patrick Blessington disagreed, saying the judge was required to tell the jury that Avery has pleaded guilty. He said he would not be calling Avery as a witness.

Sarmina said she would rule before the trial begins on Monday. Another priest and a former archdiocese school teacher will be tried at a later date.

(Editing By Barbara Goldberg and Cynthia Johnston)