The Rev. Janet Edwards acted within the Presbyterian Church (USA)'s understanding of the Bible and church law when she presided at the marriage of a lesbian couple, the defense argued yesterday during the first day of her church trial.

The Rev. Edwards, a parish associate at the multi-denominational Community of Reconciliation in Oakland, conducted the ceremony in 2005 in McKees Rocks. Church court rulings at the time said that ministers may bless same-sex couples but "should not" use liturgy that resembles a marriage ceremony. The Rev. Edwards admits she intended to perform a marriage, but says that "should not" doesn't mean "must not."

About 150 people attended the hearing before nine judges at The Priory, a North Side hotel.

The Rev. Edwards is charged with "knowingly and willfully" committing "an act of defiance" against Scripture and the church's constitution by performing a "purported marriage ceremony." The church's constitution defines marriage as a union between a man and a woman.

John Matta, a former stated clerk -- or expert on church law -- for Pittsburgh Presbytery was yesterday's only prosecution witness. In 2004, the Rev. Edwards asked him a hypothetical question about a request for a same-sex marriage, he said.

He recalled telling her that, "In my opinion, she could perform a blessing ceremony but not a marriage."

The Rev. James Evans, a member of the prosecution team, read from a text that the Rev. Edwards had submitted. It included statements like "it is my honor to officiate at the marriage of Brenda and Nancy."

The defense argued that the Bible contains ideas about sex and marriage that the church no longer upholds.

Heather Reichgott, a doctoral student in theology at the Graduate Theological Union in Berkeley, Calif., said the Bible contains many norms for marriage, including a requirement that a childless widow marry her dead husband's brother and a command for rapists to marry their victims.

"None of these are laws we follow today," she said.

Ms. Reichgott drew chuckles when she argued that "unnatural acts" are not always sinful.

"Resurrection is very contrary to nature," she said.

The Rev. Christopher Elwood, professor of historical theology at Louisville Presbyterian Theological Seminary, said that a core church document, the Westminster Confession of Faith, defined marriage as between "one man and one woman" because of 17th-century sects that promoted polygamy.

"That language, of one man and one woman, was intended to specify the number of partners, not the gender," he said.

The final witness was retired Pennsylvania Superior Court Judge Justin Johnson, a former member of the highest court of the Presbyterian Church (USA).

The language that a presbytery "shall not allow" same-sex marriage ceremonies and that it "would not be proper" for a minister to perform them is not a prohibition, he said.

"Should not" means "strongly not recommended, which is something less than mandatory," he said.

He said that an April ruling of the church's high court did prohibit same-sex marriage ceremonies, but that it could not be applied retroactively to the Rev. Edwards.