A diverse group of Maryland religious leaders launched a coalition Wednesday that organizers vowed would steadfastly resist the legalization of same-sex marriage in the 2012 legislative session.

“We will not lie down in the face of renewed efforts to redefine this institution,” said Derek McCoy, the leader of the new Maryland Marriage Alliance, which held a pair of news conferences at churches in Prince George’s County and Baltimore. “Marriage is defined as between one man and one woman.”

Many of the news conference participants were part of the lobbying effort last session that ended in the defeat of a same-sex marriage bill in the House of Delegates after it narrowly cleared the Senate.

Organizers said they are now banding together to better coordinate efforts against what could be a tougher fight in the coming months: Gov. Martin O’Malley (D) has pledged to sponsor next year’s bill and put the full weight of his office behind it.

Supporters of same-sex marriage have also stepped up their efforts, which have included a series of Web ads featuring O’Malley and other high-profile supporters of the legislation.

Sam Offer, a member of the faith caucus of Marylanders for Marriage Equality, which supports the measure, said Wednesday that opponents have not cornered the market on religious leaders.

“The religious and faith community in Maryland is divided on the issue of marriage equality,” said Offer, an associate pastor of Unity Fellowship Church in Baltimore. “People of all walks of life, including committed gay and lesbian couples, want their children to live in a stable, loving home and be protected under the law.”

The new coalition working to defeat next year’s bill has the backing of the Maryland Catholic Conference and the National Organization for Marriage, two groups that lobbied to defeat the legislation this year.

At the first of the two news conferences Wednesday, outside St. Stephen Baptist Church in Temple Hills, several speakers touted the role that churches played in defeating the bill, particularly in Prince George’s.

Victor Kirk, senior pastor of Sharon Bible Fellowship Church in Lanham, said he and others are prepared to do battle again.

“With all humility, let me say: Bring it on,” Kirk said. “Today, we ask the people of Maryland to rise up again in the defense of marriage.”

Same-sex marriage is legal in six states and the District.

If a bill passes in Maryland, both sides expect opponents to take advantage of a process that allows citizens to petition just-passed laws to the ballot. That would lead to a statewide referendum on the issue in November 2012.