BOSTON (AP) – Attorney General Thomas Reilly, who played a key role in state efforts to fight the legalization of same-sex marriage a year ago, now says he favors same-sex marriage and will oppose any efforts to ban it.

Reilly, an unannounced Democratic candidate for governor, told The Boston Globe he was “moved” by the same-sex marriages that took place after same-sex marriage was legalized on May 17.

Reilly said he would vote against a constitutional amendment to ban same-sex marriage if it reached the 2006 state ballot.

“Once rights are given, they should not be taken away,” Reilly said.

Reilly said he still personally believes marriage is between a man and woman. He also declined to take a position on whether a proposed constitutional amendment banning same-sex marriage should go before voters, saying that’s up to legislators.

Reilly is the state’s top lawyer and in that role fought same-sex marriage supporters in the Goodrich case, which led the Supreme Judicial Court to legalize same-sex marriage. He also joined with Republican Gov. Mitt Romney in enforcing a 1913 law that barred out-of-state same-sex couples from marrying in Massachusetts.

His legal brief in the SJC case questioned whether gay and lesbian parents are as good parents as heterosexual parents, language he removed after same-sex marriage supporters protested. He also criticized the SJC ruling, saying a momentous change in social policy should be left to the Legislature.

Reilly told the Globe he has been consistent since March in saying he would not favor taking away marriage rights once they were granted.

“This is not a change in my beliefs. I have been consistent,” he said. “What has changed is that May 17 came and went, and people entered into marriage. … No one has been hurt.”

He added, “You couldn’t help but be moved by the commitments and marriages that people have entered into.”

Tim O’Brien, the executive director of the state Republican Party, said Reilly has “completely flip-flopped” on the issue because he needs to answer to a special-interest group within the Democratic Party.

Arline Isaacson, co-chair of the Massachusetts Gay and Lesbian Political Caucus, said it was disturbing that Reilly would not oppose efforts to place what she says is a civil rights issue on the ballot.

“If he is now saying that he doesn’t believe our rights should be taken away, we welcome that, but we need someone who would play a leadership role in this debate and stand up and say … that a civil rights question should not be placed on the ballot,” she said.

Susan Ryan-Vollmar, editor of Bay Windows, New England’s largest GLBT newspaper, said members of the state’s GLBT community remain “furious” with Reilly.

“When the subject comes up of Reilly running for governor, it runs from, ‘Over my dead body’ to ‘He is going to have to really grovel,’” she said.

Reilly is seeking to meet with GLBT leaders as he prepares his campaign for next year’s governor’s race. Former Democratic National Committee chair Steve Grossman is trying to set up meetings between Reilly and GLBT leaders at his Newton home.

“I have an enormous respect for Tom Reilly that he is willing to move to a new position on this issue and others,” Grossman said. “I don’t want a governor who will dig in and say, ‘I will never change.’”