The sentence was resolutely bland and nicely hidden in a long Supreme Court decision issued on the last day of the term.

All it said was this: “Our decisions have declined to distinguish between status and conduct in this context.” But the context mattered. Justice Ruth Bader Ginsburg, writing for the majority, was talking about laws affecting gay men and lesbians.

Slipping that thought into a case about the treatment of a Christian student group reminded some of a technique perfected by Justice William J. Brennan Jr., whose fellow justices were wary of his “time bombs.”

“Brennan’s colleagues learned to watch for the seemingly innocuous casual statement or footnote — seeds that would be exploited to their logical extreme in a later case,” Seth Stern and Stephen Wermiel wrote in a new biography of the justice to be published in October.

Justice Ginsburg’s bland talk about status and conduct was significant because courts are more apt to protect groups whose characteristics are immutable. Calling sexual orientation a status may not require the conclusion that being gay is immutable rather than a choice, but it certainly suggests it.

There was something broader going on, too, said Suzanne B. Goldberg, a law professor at Columbia.

“The court is talking about gay people, not homosexuals, and about people who have a social identity rather than a class of people who engage in particular sex acts,” Professor Goldberg said.

Lawyers for couples challenging California’s ban on same-sex marriage wasted no time in offering the judge hearing their case a translation of Justice Ginsburg’s sentence.

“The Supreme Court definitively held that sexual orientation is not merely behavioral, but rather, that gay and lesbian individuals are an identifiable class,” Theodore J. Boutrous Jr. wrote the next day to Chief Judge Vaughn R. Walker of the Federal District Court in San Francisco.

Charles J. Cooper, a lawyer for some of the defendants in the California case, said his opponents were reading far too much into the Supreme Court decision.

“The isolated, out-of-context statements quoted by plaintiffs suggest at most that discrimination based on homosexual conduct is, in certain contexts, a reasonable proxy for discrimination against gays and lesbians,” Mr. Cooper wrote to Judge Walker.

“But even assuming that this unremarkable proposition somehow points to a behavioral definition of homosexuality,” he went on, “it by no means follows that homosexual behavior is immutable.”

But if the plaintiffs’ reading is correct, Justice Ginsburg’s statement is both a time bomb and a tea leaf that will figure in litigations concerning same-sex marriage on two coasts. Judge Joseph L. Tauro of the Federal District Court in Boston issued two rulings on July 8 striking down part of the federal Defense of Marriage Act of 1996, and Judge Walker is expected to rule soon in the California case.

As the cases make their way to the Supreme Court, any signal from the justices is bound to be analyzed and scrutinized.

“Particularly in gay rights cases, the court has chosen its words with care over a long period of time,” Professor Goldberg said. “If read properly, this decision should have an impact all over gay rights jurisprudence both because of the specific rejection of the status-conduct distinction and the shift in tone.”

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