WASHINGTON » The Supreme Court’s order last week halting same-sex marriages in Utah was two sentences long. It was provisional and cryptic, and it added nothing to the available information on where the Supreme Court stands on the momentous question of whether there is a constitutional right to same-sex marriage.

Utah’s briefs were another matter. They were expansive, and they gave a state-of-the-art account of the current arguments for denying gay and lesbian couples the right to marry.

In the trial court, the state had argued that restricting marriage to a man and a woman would make heterosexual couples act more responsibly when they had sex. In the Supreme Court, the state threw that "responsible procreation" argument overboard in favor of one focused on "optimal parenting." By the time it filed its final brief last Monday, the state had introduced a fresh argument, drawn from the Supreme Court’s decisions on affirmative action.

The state’s first argument, made before Judge Robert J. Shelby of the U.S. District Court in Salt Lake City, was that "the traditional definition of marriage reinforces responsible procreation." The government benefits that come with marriage, the state said, encourage opposite-sex couples to form stable families "in which their planned, and especially unplanned, biological children may be raised."

Shelby agreed, saying the argument was true as far as it went. Encouraging marriage would make it more likely that the children of heterosexual couples would have parents who were married.

But there was no reason, the judge went on, to think that allowing same-sex couples to marry would change that. To the contrary. By forbidding gay and lesbian couples from marrying, he wrote, "the state reinforces a norm that sexual activity may take place outside of marriage."

In the Supreme Court, state officials changed tack. They pressed a different argument, one built on a contested premise.

"A substantial body of social science research confirms," the brief said, "that children generally fare best when reared by their two biological parents in a loving, low-conflict marriage."

Lawyers for the couples challenging Utah’s ban on same-sex marriage responded that the assertion "is not true." For evidence, they cited "the scientific consensus of every national health care organization charged with the welfare of children and adolescents," and listed nine such groups. The view of the groups, the challengers said, "based on a significant and well-respected body of current research, is that children and adolescents raised by same-sex parents, with all things being equal, are as well-adjusted as children raised by opposite-sex couples."

Utah responded that it would not be swayed by "politically correct trade associations," referring to, among others, the American Academy of Pediatrics, the American Medical Association and the American Psychiatric Association. "We are not ruled by experts," the state’s brief said.

As with the argument about responsible procreation, it is possible to accept the state’s position that children are best off raised by their biological parents and yet wonder how denying gay and lesbian couples the right to marry makes that more likely. Utah argued that the two things are linked.

"By holding up and encouraging man-woman unions as the ‘preferred’ arrangement in which to raise children," the state said, "the state can increase the likelihood that any given child will in fact be raised in such an arrangement."

Shelby had rejected the argument as illogical and counterproductive. Utah’s ban on same-sex marriage, he wrote, "does not make it any more likely that children will be raised by opposite-sex couples." But it certainly demeans and humiliates the thousands of children being raised by same-sex couples in the state, he said.

In the Supreme Court, Utah refined its argument.

"The state does not contend that the individual parents in same-sex couples are somehow ‘inferior’ as parents to the individual parents who are involved in married, mother-father parenting," the state said.

But, drawing on Supreme Court decisions endorsing the value of diversity in deciding who may attend public universities, the state now said it was pursuing "gender diversity" in marriages. "Society has long recognized that diversity in education brings a host of benefits to students," the brief said. "If that is true in education, why not in parenting?" The Supreme Court did not take a position on Utah’s several shifting arguments, saying only that it would stay Shelby’s decision while an appeals court considers the case. That will happen over the next couple of months, and the state’s position may evolve further.

Or perhaps it will return to the candor of Stanford E. Purser, a lawyer with the state attorney general’s office. Shelby asked him on Dec. 4 whether letting same-sex couples marry was of "any relevance at all" to the state’s interests in encouraging opposite-sex couples to marry.

"It may end up that there is no difference," Purser said. "It may end up that there is. We just simply don’t know."