WASHINGTON — Life moves fast these days, and so does the law.

In the civil rights era, the Supreme Court waited decades to weigh in on interracial marriage. On Friday, by contrast, the court did not hesitate to jump into the middle of one of the most important social controversies of the day, agreeing to hear two cases on same-sex marriage.

By taking both, the court gave itself the chance to issue a sweeping ruling that would cast aside bans on same-sex marriage nationwide. But the speed with which the court moved also raised the possibility of a split decision, one that would provide federal benefits to same-sex couples married in states that allow such unions but would permit other states to forbid gay and lesbian couples from marrying.

Gay rights advocates said they were optimistic that the time had come for marriage equality across the nation.

“We are at a major turning point in the arc of gay and lesbian rights,” said Suzanne B. Goldberg, a law professor at Columbia. “The cases are moving fast, and the country is as well.”