Judge Mary Jacobson gave both sides time to provide more information in writing and said that she would not rule on the issue before September.
Kevin Jesperson, a state assistant attorney general, told the judge that the federal government should recognize New Jersey civil unions as the equivalent to marriage and give registered couples access to Social Security survivor benefits, joint tax filing and other federal benefits. If federal agencies don't do that, he said, the plaintiffs should sue them, not the state.
Larry Lustberg, a lawyer for Garden State Equality and a group of gay couples already suing for the right to marry, said the state can solve the potential problem by allowing gay couples to marry.
"It is the state, not the federal government that is the source of the problem here," he said.
Jacobson asked Lustberg whether she has the authority to legalize gay marriage. She also questioned Jesperson's notion that there's nothing the state can do to make sure residents get fair treatment from the U.S. government, saying "it would not be so far-fetched" for judges to take action to protect New Jersey citizens.
She also lamented a shortage of on-point case law cited by either side.
In 2006, New Jersey's Supreme Court ruled that gay couples should be treated equally under the law as married couples. The Legislature responded by creating civil unions, which seek to give the legal protections of marriage without calling it marriage.
Six couples and several of their children sued in 2011, saying civil unions fall short of that promise. That case is at least several months from going to trial.
But last month the couples asked the court to make a judgment before trial in light of the June U.S. Supreme Court ruling that invalidated key parts of the Defense of Marriage Act, which had banned the federal government from recognizing gay marriage.
They say there's a new urgency because state law is blocking citizens from receiving full federal benefits.
Jesperson said it's not clear yet to what degree that will happen since federal agencies are just starting to roll out regulations for how they'll treat same-sex couples.
So far, agencies have said that they will extend benefits to couples who are married. Some have said that only couples in marriages recognized by the state where they live will be eligible. Others, like the Department of Defense, have determined that they'll recognize marriages that are legal where they were granted.
If the state wins this round in court, a trial is still expected on the question of the equality of civil unions.
New Jersey lawmakers passed a bill to recognize gay marriage last year, but Gov. Chris Christie vetoed it. Gay rights groups are pushing lawmakers to override the veto by January.
Thirteen states in the U.S. have same-sex marriages, with New Jersey and Pennsylvania the only Northeastern states not among them.
