TRENTON, N.J. – The battle over gay marriage reached New Jersey’s Supreme Court yesterday, with justices grilling lawyers about why the state should prevent homosexual couples from marrying and questioning whether expanding such rights could lead to the recognition of polygamous unions.

The arguments came in the case known as Lewis v. Harris, in which seven long-time gay couples sued the state in 2002, claiming the state constitution affords them the right to marry.

Nationally, only Massachusetts allows gay marriage. Two other states – Hawaii and Vermont – have found that homosexual couples have constitutional rights to the same legal treatment as straight couples. While conservative groups filed documents with the New Jersey court contending that allowing same-sex marriage would harm society, a state deputy attorney general, Patrick DeAlmeida, said it is the job of elected lawmakers, not a panel of judges, to decide the issue.

“To allow same-sex couples to marry would not be removing a barrier to marriage, but redefining marriage itself,” he told the seven-member court.

Mr. DeAlmeida fielded the brunt of the judges’ questions, including what might be protected by preventing same-sex marriage in New Jersey, one of 16 states where it’s specifically illegal to discriminate based on sexual orientation. The state also has no legal barriers for same-sex couples to adopt children and recognizes domestic partnerships, although those do not offer all the legal protections of marriage.

“The Legislature has an interest in protecting the institution of marriage,” Mr. DeAlmeida responded. A chief justice, Deborah Poritz, retorted, “It’s not as if the institution of marriage hasn’t changed in rather dramatic ways.”

The attorney for the seven couples, David Buckell, talked about the personal stories of some of his clients. “How do plaintiffs answer their children’s questions about why they are not married?” he said. “The only answer is that the state does not think their relationships are worthy.”