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.