PITTSBURGH - Two Boston priests are defrocked for their role in a pedophilia scandal; a Pittsburgh priest is excommunicated when he leaves the church to start his own ecumenical congregation; and a panel of bishops debate denying communion to Massachusetts Sen. John Kerry and other politicians who don't oppose abortion.

Such terminology sends even experts leafing through the Roman Catholic Church's canon law, and leaves many lay believers and outside observers scratching their heads.

Among these three forms of church discipline are myriad shades of gray about what experts say church officials can and should do when highly visible members of the flock stray from church teaching.

"There's kind of a hierarchy of things that can happen if you're doing something gravely sinful - one is denial of the sacraments and the next step would be excommunication," said Jimmy Akin, director of apologetics and evangelization for Catholic Answers, a San Diego nonprofit that explains and defends church doctrine.

Excommunication is a declaration that someone is outside the church. It can be imposed privately and, in rare cases, after a church tribunal. But it usually happens automatically and publicly, as it did when the Rev. William Hausen broke with the church to establish his Christ Hope Ecumenical Catholic Church in a suburban Pittsburgh hotel banquet room this month.

"You no longer participate in the Catholic Church by your own free choice," said the Rev. Ronald Lengwin, spokesman for the Pittsburgh diocese. "We did not throw anybody out of the church."

Under canon law, Hausen cannot preside at Catholic Masses or services, hold church office, nor can he dispense or receive church sacraments, Akin said, unless Hausen were to renounce his new church and be granted reinstatement.

"But this is not a judgment upon a person's soul or whether they've committed a sin or not," said the Rev. Larry DiNardo, the diocesan lawyer who issued the excommunication decree against Hausen. "This is an external judgment on whether they want to be part of the Catholic church."

"Excommunication is seen as a punishment, but also as a way to nudge a person to reform their life," said the Rev. Thomas Reese, editor-in-chief of the Jesuit magazine America. "It's to tell them that what you're doing is so serious as to put yourself outside the church."

What's trickier are situations like those involving the Boston priests or Kerry.

The Revs. Ronald Paquin and Paul Shanley were defrocked for alleged sexual misdeeds. Paquin, 61, pleaded guilty in 2002 to raping an altar boy and has been named in 24 civil sexual abuse lawsuits. Shanley, 73, has pleaded innocent to charges he raped four men at a parish in the 1980s and is awaiting trial in October.

Defrocking - or laicization, the preferred term of the church - means they no longer have priestly powers, though both men remain Catholics.

To Catholics, that's a key distinction. Although Hausen is outside the church, the church still recognizes him as having some priestly powers, most notably the ability to consecrate bread and wine into the body and blood of Christ, DiNardo said.

When Hausen offered communion at his new church, that sacrament was still considered "valid" by the church - meaning the bread and wine really were changed - even though it wasn't "licit," or legal, under church law, DiNardo said. In fact, it's because Hausen still has that power that the church finds his actions more troubling, Akin said.

Kerry's situation is different because he's a lay person without any official church powers - and it's confusing because although administering or having an abortion is grounds for excommunication, advocating abortion rights probably isn't.

"Most canon lawyers would say that would not be grounds for excommunication," Reese said of Kerry's pro-abortion stance. "If you're running an abortion clinic, that's something else."