The moment came less than a week after voters in Maine, like those in 30 states before it, rejected same-sex marriage, and just a day before New York legislators would again postpone consideration of a bill to legalize such weddings, conceding inadequate support.

And it underscored what a fascinating example Ms. DeGeneres is setting, not to mention how tough it is to figure out precisely where Americans stand on an issue so fiercely contested that the Roman Catholic Archdiocese of Washington, D.C., said last week that it would scale back social service programs if the district legalized same-sex marriage.

In the handful of states where same-sex marriage is legal, legislatures and courts — not voters — have made it so. A few polls in recent months have suggested that while a majority of Americans believe that gay couples should be able to enter into unions with some of the legal protections of marriage, a minority believe that gays and lesbians should be permitted to “marry,” per se. Same-sex marriage doesn’t fit into the kind of family that many Americans believe should be idealized; it offends many others’ deeply felt religious principles.

And yet Ms. DeGeneres, who exchanged vows with Ms. de Rossi during a span last year when same-sex marriage was legal in California, seems more popular than ever — and among audiences squarely in the mainstream.

A decade ago, she had trouble getting work, a development that she and many observers chalked up to her being “the most famous lesbian in the world,” as Ms. de Rossi described her on “Oprah.”