Sarah Dowling, who lives outside Portland, Maine, has been waiting for almost two decades to marry her girlfriend. A sign of hope that voters will give her that right hangs in her closet: a new wedding dress.

“It’s hard not to be optimistic,” said Dowling, 54, a social worker. “I know so many people who have moved from a not-supportive stance to a supportive one.”

In Maine, Maryland and Washington, voters on Nov. 6 will decide whether to allow gay men and lesbians to wed. The issue is drawing the broadest public support to date and surveys show the measures leading in all three states -- giving advocates their best chance yet for the first ballot-box victory after a decade of defeat.

About half of Americans say gay marriage should be legal, according to national polls. A June 28-July 9 poll by the Washington-based Pew Research Center found that 48 percent of Americans favor same-sex marriage, with 44 percent opposed. That’s a reversal from 2009, when they opposed it 54-37 percent.

“The increase in support for same-sex marriage has been quite rapid over the past four years, a much steeper rise than we saw over the previous eight years that we’d been tracking this,” said Scott Keeter, the director of survey research for Pew, a nonpartisan group, in an interview. “Most analysts of public opinion expected this growth in support to happen, although perhaps not as fast as it actually did.”

Voters have rejected same-sex marriage in all 32 states where it has appeared on the ballot, including in Maine in 2009. The unions are legal in six states and the District of Columbia because of court rulings and measures approved by public officials.

“The most important thing we can do is take the talking point away from opponents of marriage equality that we have consistently lost at the ballot box,” said Fred Sainz, a spokesman for the Human Rights Campaign in Washington, in an interview.

Advocates on both sides say the state contests will be close, and that opinions may shift over the next month as political advertising becomes more frequent.

The Maine gay marriage measure was leading 53-43 percent, according to a poll by the nonprofit Maine People’s Resource Center. In Maryland, an OpinionWorks survey showed it leading 49-39 percent.

In Washington, the gay marriage measure led 51-37 percent, according to an Elway Research poll.