PORTLAND – The leader of Maine’s Roman Catholic diocese issued a letter to be read at weekend Masses opposing gay marriage.

Bishop Richard Malone’s letter calls on Catholics to work to preserve the traditional sacrament of marriage by opposing efforts to legalize same-sex marriage.

“To redefine marriage to include same-sex couples is to strip marriage of an essential component, namely the ability and obligation to procreate,” the bishop said in his letter. “To strip marriage of this essential component is to render marriage meaningless and open it up to endless revision and redefinition.”

The letter appeared days after a group of Maine ministers from different faiths announced their support for gay marriage. Members of the Religious Coalition for the Freedom to Marry in Maine held news conferences Thursday.

It also follows referendums in California, Arizona and Florida in which same-sex marriage bans were imposed. The votes have been followed by demonstrations around the country, including one Saturday in Portland’s Monument Square.

Maine law defines marriage as the union of a man and a woman. The state’s Constitution does not have a provision that defines marriage. Maine does have a domestic partnership registry that is open to gay couples.

Malone’s letter said the church will be launching initiatives in the weeks and months ahead to preserve and support marriage as it is currently defined. It said objections to same-sex marriage are not based strictly on religious principles, but also on what is best for society.

EqualityMaine, which advocates on behalf of gay and lesbian Mainers, said it gathered more than 33,000 names and addresses on Election Day in support of marriage for same-sex couples. The Religious Coalition for the Freedom to Marry in Maine, which includes 120 religious leaders of 14 faiths, will be listed on postcards sent to legislators, EqualityMaine said.

“We have started the conversation with voters because what we know is we have to change the hearts and minds of voters and that takes some significant amount of time,” said Betsy Smith, executive director of EqualityMaine.