PORTLAND — The Roman Catholic Diocese of Maine will take no active role in a political campaign against a same-sex marriage referendum that’s expected to be on the November ballot, Bishop Richard Malone announced today.

Instead, the diocese is expanding an existing educational program to better inform church members about the qualities and benefits of marriage between one man and one woman.

Malone issued a pastoral letter on marriage today that will be used extensively to teach 185,000 Roman Catholics in Maine about the gift of traditional marriage and the need to preserve it as it is.

“We are going to ask them to reconsider their understanding of what marriage is,” Malone said during a news conference this afternoon.

Malone said he and other church leaders “haven’t done a good job” providing this type instruction to its members in the past, so many Catholics aren’t informed about the “true nature of marriage.”

The letter, published as a report on glossy paper, explains “the fullness of marriage” using Bible passages, “2000 years of Christian teaching ” and “reason and natural law.”

Malone said the diocese doesn’t want to impose a law or belief on anyone, but it does want to make the church’s position known and contribute to the public debate over the push to redefine marriage.

“It’s our constitutional right to make our voices heard,” he said.

The pastoral letter will be distributed through Catholic schools and churches across the state, posted on the diocesan website and published in its Harvest magazine in May. It also will be the subject of church discussion groups and radio broadcasts.

Malone said the information is meant for parishioners, “but we’re hoping the message gets out beyond.”

The largely in-house educational initiative represents a significant departure from the major role that the diocese played in supporting a successful 2009 referendum against gay marriage. The diocese contributed more than $500,000 to that $3.8 million campaign and its public affairs director took a leave of absence to lead the effort.

This time, Malone said, the diocese won’t be taking up special collections, buying TV ads or contributing staff to a political campaign against same-sex marriage.

He said that the educational initiative will be covered by the church’s educational budget and that no specific funding has been dedicated to the effort. He said he didn’t know how much it cost to publish and distribute the pastoral letter on marriage.

He described Brian Souchet, appointed last November to be director of the diocesan Office for the Promotion and Defense of Marriage, as a volunteer. Souchet was parish outreach coordinator for the 2009 campaign against gay marriage.

Souchet said the diocese is taking the long view in its efforts to preserve traditional marriage. The educational program is aimed at one-quarter of active Catholics in particular who “don’t quite get” the church’s teachings on marriage.

“No matter what happens in November, this issue isn’t going away,” Souchet said. “We need to keep teaching as a church. To continue to just fight the November battles is shortsighted.”

Last month, same-sex marriage advocates in Maine turned in more than enough signatures to put a gay-marriage question on the November ballot.

First, the question will be considered by a Republican-controlled Legislature and Republican governor. If both approve the measure, then same-sex marriage would become legal. If either rejects the measure, which is expected, the state will hold a referendum.

The Freedom to Marry Coalition has already formed, representing about 20 groups that support same-sex marriage, including EqualityMaine, the Maine Women’s Lobby and the Religious Coalition Against Discrimination, said spokesman David Farmer.

“The opposition’s campaign may be different this time, but we believe they will have an organized, well-thought-out and well-funded campaign,” Farmer said. “And so will we.”

Supporters of gay marriage spent $5.8 million on the 2009 campaign.

“We’re going to run a pro-active campaign to explain why marriage matters for same-sex couples, which are the same reasons as other couples,” Farmer said.

Opponents of gay marriage are poised to file paperwork with the Secretary of State next week, establishing a political action committee or a ballot question committee that will be called Protect Marriage Maine, said Carroll Conley Jr., executive director of the Christian Civic League of Maine.

Conley said the opposition has a “great rapport” with Bishop Malone and support his plan to educate Catholics about the importance of traditional marriage.

“This campaign will benefit from their effort,” Conley said. “Would it be our preference to have them formally involved in the campaign? Absolutely.”

Conley said his organization will be soliciting donations and campaign assistance from Catholics across the state.

Same-sex marriage is allowed in Massachusetts, New Hampshire, Connecticut, Vermont, New York, Washington, Iowa, Washington, D.C., and Maryland. Civil unions for same-sex couples are allowed in Rhode Island.