“We do have a big hill to climb to be able to effectively communicate our message,” Brown said. “But we don’t need to match the other side — we win repeatedly while being outspent.”

All four states are expected to be carried in November by President Barack Obama, who came out in support of same-sex marriage earlier this year.

In Maryland, as in Maine and Washington, the most recent polls show a lead for the supporters of same-sex marriage. But comparable leads in other states — notably in California in 2008 — evaporated by Election Day, and Josh Levin, manager of the Marylanders for Marriage Equality campaign, expects the final result to be extremely close.

Levin and his allies are aware that Maryland, because its polls close earlier than Maine’s or Washington’s, could become the first state to approve same-sex marriage by popular vote.

“We cannot take it for granted,” Levin said. “That being said, if we make it happen in Maryland, the lessons learned here can be applied across the country.”

The campaign has been intensifying in recent weeks, widening rifts among Maryland’s most prominent Catholics, among black clergy, even among NFL teammates. Baltimore Ravens linebacker Brendon Ayanbadejo has endorsed same-sex marriage; center Matt Birk wrote a newspaper column opposing it.

The divide among Catholics — the state’s largest denomination — has been striking. Archbishop William Lori and the Maryland Catholic Conference are actively campaigning against same-sex marriage. Catholic VIPs supporting it include Gov. Martin O’Malley and former Lt. Gov. Kathleen Kennedy Townsend, daughter of the late Robert F. Kennedy.

In both Maryland and Washington state, voters are being asked to approve or reject a same-sex marriage bill passed by the legislature earlier this year. In each case, opponents were able to collect enough signatures to challenge the laws.

O’Malley, who played a key role in winning legislative support, says the law has strong provisions to protect the religious freedoms of the Catholic Church and other faiths that disapprove of same-sex marriage.

“We’re a people of many different faiths, and it’s so important that we protect rights equally under the law,” he said.

Among several openly gay legislators who helped advance the bill was Delegate Heather Mizeur, who married her lesbian partner during a brief window when same-sex marriage was legal in California in 2008.

Mizeur says she’s a dedicated Catholic, despite her opposition to church teaching on marriage.

“The No. 1 tenet of our faith is the primacy of our conscience,” Mizeur said. “That was important to me as a young person, sitting there trying to pray the gay away.”

Another churchgoing Catholic active in the gay-marriage campaign is 83-year-old Erma Durkin of Glen Arm, whose gay son married his longtime partner in New York last year. Durkin said she’s made clear to her pastor that she objects to materials inserted in the church bulletin conveying the Catholic hierarchy’s opposition to same-sex marriage.

“You can’t command that someone stay celibate and single all their life,” Durkin said. “If we find someone we love that much that we want to marry, that’s a wonderful thing.”

On the other side, Archbishop Lori recently hosted a meeting of same-sex marriage opponents to mobilize for the campaign’s home stretch.

“The union of man and woman is not only a good for the couple, but for the entire community of believers and for humanity,” Lori told the gathering.

Within the opponents’ coalition, the Maryland Marriage Alliance, black pastors are playing a key role. One of them, the Rev. Derek McCoy, is the campaign chairman; he is keenly aware of the high stakes.

“Eyes are on us from around the country,” he said. “We have a gargantuan task ahead of us.”

Blacks comprise about 25 percent of Maryland’s electorate, and polls showed a significant increase in their support of same-sex marriage after it was endorsed in May by Obama and the Baltimore-based National Association for the Advancement of Colored People.

“The question isn’t if marriage equality will prevail — the only question is when,” said Ben Jealous, the NAACP’s president. “The rising generation of young voters is the most diverse and inclusive we’ve seen. It’s only a matter of time until the laws catch up with them.”

McCoy believes most Maryland blacks still oppose same-sex marriage and said one of his coalition’s challenges is persuading them to vote “No” in the referendum even if they support Obama.

“Some people are in a quandary,” he said, “We’re telling them, ‘Don’t vote against your conscience.’”

The Rev. Delmon Coates, pastor of a large, predominantly black Baptist church in Prince George’s County, has taken up the banner on the other side. He recently brought national civil rights leaders, including the Rev. Al Sharpton, to the region to endorse same-sex marriage.

As in Maryland, the campaign in Washington state involves a measure signed into law by a Catholic governor, Christine Gregoire, and now being challenged by gay-marriage foes.

The coalition supporting gay marriage has raised more than $8.9 million, compared to about $1.7 million for the opponents. The biggest single donation in support of the law came from Amazon.com CEO Jeff Bezos and his wife, MacKenzie, who donated $2.5 million in July.

Maine’s ballot measure marks the first time that gay-rights supporters — rather than opponents — have chosen to put same-sex marriage before voters. A gay-marriage law passed by the legislature in 2009 was quashed that fall after opponents gathered enough signatures for a referendum; this year, gay-marriage supporters used the same tactic to give voters a chance to reconsider.

The political action committee backing same-sex marriage in Maine raised about $3.4 million through September, compared to $430,000 for the leading opposition PAC.

At stake in Minnesota is a proposed amendment that would strengthen the existing law against same-sex marriage by inserting it in the state constitution. If the amendment is defeated, it would still take a legislative act, court ruling or future popular vote to legalize gay marriage.

The main group opposed to the amendment raised $7.8 million by the end of September. The leading group supporting it raised about $2 million, nearly half of that from Catholic dioceses and affiliated organizations.

A Minneapolis Star Tribune poll last month found 49 percent of likely voters supporting the amendment and 47 percent opposing it, within the poll’s margin of error.

In all four states, TV ads airing against same-sex marriage are the brainchild of political strategist Frank Schubert, whose ads were credited with a key role in California’s passage of the Proposition 8 ban on gay marriage in 2008.

Schubert’s strategy is to laud heterosexual marriage as a timeless institution that should not be “redefined” and to warn that legalization of same-sex marriage can impinge on the rights of those who oppose it. He says such ads offer “solid lines of argument,” while his gay-rights rivals assail them as deceptive scare-mongering.

To Schubert, the four-state showdown is “a big deal” — in part because the U.S. Supreme Court is expected to take up the question of same-sex marriage soon.

“We don’t want to lose anywhere,” Schubert said. “If one state does go the wrong way, we’ll argue that this is just one of out of 36 … But we’d rather be arguing we’ve won every time it has gone before voters.”

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Associated Press writers Rachel La Corte in Olympia, Wash., Patrick Condon in Minneapolis, Clarke Canfield in Portland, Maine, and Brian Witte in Annapolis, Md., contributed to this report.

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David Crary can be followed on Twitter at http://twitter.com/CraryAP