But the movement, which believes that Jews must conserve traditions yet also holds that laws must evolve to meet the shifting realities of modern life, has long given individual rabbis in its 700 congregations in North America the authority to make many decisions for their communities under a privilege known as mara d’atra — authority for a place.

Many rabbis have capitalized on this concept to perform Jewish wedding ceremonies for gay couples, complete with a chuppa, or traditional wedding canopy, and a ketubah, or marriage contract. They say they overlook the Torah’s prohibition against homosexual sex as an ancient dictum that has lost its moral force.

The spectrum in the movement is striking, according to experts. Some rabbis staunchly resist requests to officiate at same-sex weddings, even if congregants want them, arguing that the movement should not equate homosexual relationships with heterosexual ones. Other rabbis are eager to officiate, but will not do so because their congregations are opposed. Others step out ahead of their congregations and might perform the ceremony far from the synagogue and not offer blessings for the couple at a Sabbath service. New York’s law prohibits any penalties for clergy members who refuse to perform same-sex weddings.

Those rabbis who do perform same-sex ceremonies improvise the language. When Rabbi Jeremy Kalmanofsky, 45, the leader of Temple Ansche Chesed on the Upper West Side of Manhattan, performed a wedding for two men several years ago, he eliminated some phrases from the traditional Jewish service, using “loving companion” instead of terms like bride and groom. He sees such changes as a “creative betrayal of tradition” by “finding ways to sanctify love and commitment.” But he insisted that some elements from the traditional ceremony remain ironclad, like commitments to sexual exclusivity and mutual care.

“If Jewish communities are to affirm what has, until now, been an outlawed sexuality, it must be because we have come to see that gay relationships can conform to our deepest vision of human relationships, as expressed in norms of love, commitment, mutuality and family,” he wrote on his blog Honest to God.

On the morning after Gov. Andrew M. Cuomo signed the same-sex marriage bill, his synagogue celebrated the bat mitzvah of a girl raised by lesbian parents.