Given the recent flurry of states saying "I do" to same-sex marriage, nationwide legalization is "a sure thing," says the executive director of the American Civil Liberties Union.

"Clearly, the momentum is on our side," says Anthony Romero, 43, the first openly gay person (and first Puerto Rican) to head the ACLU in its 89-year history. "It's just a matter of time."

Just last week, Maine's legislature voted to legalize gay marriage, New Hampshire passed a law that awaits the governor's signature, and the District of Columbia voted to recognize out-of-state unions.

Massachusetts, Iowa, Vermont, and Connecticut allow gays to marry. In California, the state Supreme Court will rule on the repeal of Proposition 8, which bans gay marriage.

A Pennsylvania statute prohibits same-sex marriage, but two legislative efforts to add a state Constitution amendment banning such unions failed. In New Jersey, Gov. Corzine says he will sign a same-sex marriage bill if one reaches his desk.

Romero is expected in town today to discuss the current outlook on homosexual rights at the annual meeting of the ACLU's Greater Philadelphia chapter.

Same-sex marriage is nothing new to the 550,000-member ACLU. Its first challenge to a state law restricting matrimony to opposite-sex couples was filed in 1970 on behalf of a male duo in Minnesota. They lost.

Gay marriage remains a top priority for the ACLU, behind only national-security issues, says Romero, who began his tenure four days before 9/11.

Support for same-sex marriage is on the rise, with the latest ABC News/Washington Post poll showing 49 percent of Americans favoring legalization - up from 32 percent in 2004.

Moreover, the shift has spread across ideological lines. Approval among conservatives has tripled, to 30 percent.

G. Terry Madonna, director of the Center for Politics and Public Affairs at Franklin and Marshall College, predicts gay marriage will be legal nationally within a decade.

It make take a while for the Keystone State to join the parade, however.

"This isn't Iowa," says Madonna. "A same-sex marriage bill has zero chance of getting through the legislature in the foreseeable future. It will take a court order."

Michael Geer, president of the conservative Pennsylvania Family Institute, agrees. If an anti-gay-marriage amendment were put to a public vote, he says, it would pass.

"That's how democracy should operate," he says. "The people of Pennsylvania are being denied a voice in this issue."

The voice is changing. A new survey by Muhlenberg College's Institute of Public Opinion says same-sex marriage is making inroads in the state. Opposition fell to 51 percent from 54 percent in 2004, while approval increased seven points, to 42 percent.

Last year, a bill to amend the state Constitution to ban same-sex marriage never got to a Senate vote. In 2006, a measure passed both houses, but the two sides couldn't agree on language.

Though Geer presumes new legislation will be filed before the current session ends in November 2010, those involved in past attempts aren't rushing forward.

Sen. Michael Brubaker, a Republican representing parts of Lancaster and Chester Counties and a sponsor of last year's bill, won't back one this time, his spokeswoman says.

Rep. Babette Josephs (D., Phila.), chair of the House State Government Committee, where such a bill would land, says it's unlikely the lawmakers will take up the issue.

"It's so divisive. In this economic climate, I don't think people could care less. They're worried about their jobs, taxes, their kids' education. People's attitudes are changing."

Regardless, Pennsylvania defines marriage as a male-female alliance under the 1996 statute. Also, same-sex marriages validated outside the state are not recognized here.

Romero, who is single, has faith in Pennsylvania. "Philadelphia is the birthplace of democracy. It would be embarrassing for the state to be at the end of the curve rather than at the beginning," he says.

In New Jersey, which has had civil unions since 2006, gay-marriage advocates are optimistic that a bill will be approved by the Legislature this year. Opponents hope for a statewide vote in 2010.

As for President Obama's endorsement of marriage as male-female only, Romero promises: "We will push him. He's simply wrong. I think he'll have to come around on this.

"One wonders whether he's being politically expedient because he doesn't want to repeat the mistakes of Bill Clinton in taking on 'Don't ask, don't tell' so early."

University of Pennsylvania law professor Tobias Wolff, 39, Obama's senior campaign adviser on gay issues, has openly disagreed with the president on same-sex unions.

Nonetheless, he says, Obama invites opposing points of view and is working to build broad congressional support before pushing any gay-friendly legislation.

"It takes time, which is frustrating in light of the enormity of inequality that more than 10 million gay Americans experience under federal law," Wolff says.

Marriage is the key word in the debate, advocates say, because it confers consistent - and transferable - federal rights. Civil-union benefits vary by state and apply only to their state of origin.

"Marriage is the only legal term that carries with it that recognition," says Stephen Glassman, 58, chairman of the Pennsylvania Human Relations Commission.

In most of the world, Geer counters, that recognition is restricted to male-female duos.

"Until the last few milliseconds of history, if you spun the globe and put your finger on any land mass, marriage has been practiced between a man and a woman."

To wit, when Romero came out to his working-class Puerto Rican parents two decades ago, their reaction was neither civil nor libertarian.

Raised in the Bronx projects, he was the first in his family to graduate from high school, going on to Princeton and Stanford Law.

"They were angry and disappointed," he recalls. "I was the star son, the golden boy. For them, it was like they were meeting the first homosexual in their lives, and it was their son."

His parents eventually came around, he says, and so will the rest of the country.

The ACLU's resolve will not weaken, Romero says, despite a sharp falloff in contributions that forced 34 layoffs in January and a 19 percent budget cut for fiscal 2010, which began April 1. Still, the projected deficit could reach $7 million.

Tough odds don't faze Romero. Even when they're of biblical proportions.

"We are used to being David to the government's Goliath," he says. "We've done a pretty good job with our slingshot so far."