By Dave Warner

PHILADELPHIA (Reuters) - A criminal trial in the Philadelphia Catholic Archdiocese pedophilia scandal gets underway on Tuesday, a case likely to be watched closely as one defendant is the first high-ranking U.S. cleric to go to trial in a child sex abuse case.

Selection of a jury to hear child endangerment charges against Monsignor William Lynn and more severe sex abuse charges against two others is set to begin in Common Pleas Court.

While Lynn is not charged with sex abuse, the others on trial -- one priest and one defrocked priest -- are accused of sexually abusing children between 1996 and 1999. Another priest and a former archdiocese school teacher facing sex abuse charges will be tried separately.

The case not only puts a harsh spotlight on the Philadelphia Archdiocese, the nation's sixth largest with 1.5 million adherents, but is worthy of attention from the Vatican, given Lynn's rank as the highest U.S. church official to go to trial, experts say.

"This is cause for major anxiety in the church," said Terry McKiernan, co-director of BishopAccountability.org, a watchdog group. "Certainly this will be watched at the Vatican. This is very worrisome to them."

Typically in the sex abuse scandals that have rocked the Roman Catholic church for decades, cases have been settled out of court. Rarely --- just 30 to 40 priests out of more than 1,000 accused -- do such cases go to trial.

The church has paid out some $2 billion in settlements to victims, bankrupting a handful of dioceses.

Lynn, rather than call law enforcement or remove priests accused of misconduct from their posts, "routinely and knowingly placed abusive priests in positions where they would have continued access to children," said a grand jury report released in January 2011.

The grand jury said Lynn, 61, did so under direction of Cardinal Anthony Bevilacqua, who died on January 31 at age 88. Lynn was secretary of the clergy under Bevilacqua.

Bevilacqua, the retired archbishop of Philadelphia, was to have been a witness in the trial, after a judge ruled just a day before he died that he was competent to testify. Church officials said Bevilacqua suffered from dementia and cancer.

Given Lynn's rank, a plea bargain is likely to be under consideration, said attorney Marci Hamilton who is involved in six civil lawsuits against the archdiocese on behalf of men who say they were sexually abused as children by churchmen.

"I would be shocked if a plea was not at the top of Monsignor Lynn's list," she said. "It is very rare for any higher-ups in the Catholic Church to even testify at trial, let alone be a defendant at trial."

Typically in a plea bargain, the accused may plead guilty to certain charges so that other charges are dropped or in exchange for a reduced sentence.

If history is a guide, Hamilton noted, such a plea bargain could come at the last minute.

"They might even go through jury selection, but they will not let it get to the point where you have to testify," she said.

She too said the case would attract remarkable attention.

"I think it is going to be watched closely by the church, but I think it will be equally closely watched by prosecutors around the country," she said.

Opening statements are set to begin on March 26.

(Editing By Ellen Wulfhorst)