The Catholic bishops in each state had urged voters to uphold the traditional definition of marriage between one man and one woman and warned that religious liberties could be threatened by legalizing same-sex marriage.
Maryland and Washington voters upheld laws permitting same-sex marriage that were passed earlier in the year by their legislatures and signed by their governors, but challenged in the referendum process. Minnesotans rejected a measure to ban same-sex marriage.
Thirty other states have passed laws prohibiting such marriages. Previously six states and the District of Columbia had allowed same-sex marriages through legislative action and court rulings.
Voters in Maine approved a referendum authorizing same-sex marriage, a measure that bypassed courts and the Legislature, and reversed a 2009 referendum to ban such unions.
In Maryland, Baltimore Archbishop William E. Lori was among the most vocal leaders of the campaign to defeat the referendum, and he expressed disappointment in the vote.
"I think that vote will prove not to have been for the common good of our state," he said in a statement.
The Maryland Catholic Conference, which advocates for public policy on behalf of the state's bishops, joined the Maryland Marriage Alliance in efforts to overturn the law. Archbishop Lori praised the advocates' work over the past year.
"So much hard work went into this, and I'm very, very grateful to everyone who worked so hard," he said. "We will continue to witness to the values of marriage as understood as the union of one man and one woman, as the most sound, secure and loving way to bring children into the world."
The Catholic conference said: "Regrettably, Marylanders decided by the narrowest of margins not to repeal the law that redefines marriage."
With 97.5 percent of the Maryland vote tallied, 52 percent, or 1,208,068 voters, approved the same-sex marriage measure, compared to 48 percent, or 1,112,998 voters, who rejected it.
The language of the ballot measure "masked the fact that this law does not simply assign civil benefits to gay and lesbian couples, but drastically dismantles in our state law the fundamental family unit of mother, father and child," the conference said.
"The people of Maryland were promised that this law would protect religious institutions and individuals who believe marriage is the union of one man and one woman, and we will remain vigilant in ensuring that those promises are upheld," it added.
Bishop Richard J Malone, who is administrator of the Diocese of Portland, Maine, said in a statement he was deeply disappointed in the outcome in his state.
"I am deeply disappointed that a majority of Maine voters have redefined marriage from what we have understood it to be for millennia by civilizations and religions around the world," said the bishop, who in August was installed to head the Diocese of Buffalo, N.Y. He thanked "the Catholic faithful who did not abandon Catholic teachings on the nature of marriage."
Maine's voters, with 78.1 percent of the vote tallied, agreed to repeal the same-sex marriage ban by a vote of 53.4 percent to 46.6 percent against.
In efforts to persuade voters to oppose legalizing the marriages, the bishops of Washington had issued video statements and a pastoral statement opposing the referendum.
With about 60 percent of the vote tallied as of early the morning of Nov. 7, the vote was 52 percent in favor of allowing same-sex marriages compared to 48 percent opposed.
In Minnesota, with 99.7 percent of the vote tallied, the result was 51.3 percent, or 1,507,152 votes, to oppose a ban on same-sex marriage, compared to 47.6 percent or 1,400,396 votes to support the measure.
Archbishop John C. Nienstedt of St. Paul and Minneapolis wrote in a column in the archdiocesan newspaper, The Catholic Spirit, that the church's "effort to support God's unchanging plan for marriage is not a campaign against anyone but rather a positive effort to promote the truth about marriage as a union between one man and one woman."