Provincetown, Mass. ? A year after Massachusetts became the first state in the nation to sanction same-sex marriage, a widespread backlash has made it likely that marriage between two men or two women will remain illegal in the rest of the nation while a legal and political struggle over the definition of marriage plays out.

In the wake of the Massachusetts court ruling that led to the first legal gay marriages last May 17, more than a dozen states — including Kansas — have added amendments to their constitutions to codify marriage as a heterosexual union, and more than a dozen other states are considering similar amendments.

For opponents of same-sex marriage, last year’s wave of gay and lesbian couples exchanging vows in the Bay State — as well as weddings in San Francisco, Oregon and elsewhere that were later ruled invalid — has given their cause an urgency that it might otherwise have lacked.

“I think we’ve seen an uprising, if you will, among the American people who believe that marriage should be defined as one man, one woman,” said Peter Sprigg of the conservative Family Research Council in Washington, D.C. “So ironically, what has happened as a result of the Massachusetts decision is to strengthen the movement to define marriage.”

But a leading advocate of same-sex marriage points to past debates over divorce and interracial marriage as indicators that the country is in the midst of a transitional period that will result, in the long run, in acceptance of legal gay and lesbian unions.

“What we see is some states moving in the direction of equality faster, while others regress or even add layers of repression for a while,” said Evan Wolfson of the New York advocacy group Freedom to Marry. “Ultimately, hearts and minds open. But it’s not pretty and it’s not quick.”

In the year since the state’s Supreme Judicial Court ruling allowing same-sex marriage took effect, more than 6,100 same-sex couples have wed, representing about 17 percent of Massachusetts’ marriages in the last year.

Many gay couples who are nearing their first anniversary say that little in their day-to-day lives changed after their weddings. That is probably because the first wave of weddings generally involved couples who had already lived together for many years, gay leaders say. Massachusetts’ vital statistics registry shows that the biggest group of lesbian and gay marriage certificates went to people in their 40s.

Still, these couples note a less tangible change.

“It’s made us feel equal, at least in the eyes of Massachusetts,” said Jerry Ouellet, 55, who manages a home and garden furnishings shop on Commercial Street, Provincetown’s narrow shopping and reveling thoroughfare. “It really makes us feel whole, equal to my mom and dad and their marriage.”

Hillary, left, and Julie Goodridge play with their 9-year-old daughter, Annie, and their dog, Mary, in their back yard in Boston. Julie and Hillary Goodridge were the lead plaintiffs in the lawsuit against the state of Massachusetts that led to same-sex marriages last year.