SALT LAKE CITY - Advocates on both sides of the gay-marriage debate predicted that the U.S. Supreme Court ruling in June that overturned part of a federal ban on gay marriage would create a pathway for states to act.

They were right.

In the six months since the decision, the number of states allowing gay marriage has jumped from 12 to 18, including New Jersey, and a fight is brewing in Pennsylvania. Judges in New Mexico, Ohio, and, most surprising, Utah all ruled in favor of same-sex marriage in just the last week. Both Utah's case and one in Nevada will next be heard by federal appeals courts, putting them on a path toward the high court. Ohio's case, recognizing same-sex death certificates, also will likely be appealed.

The series of court decisions has many asking: When will the Supreme Court step in and settle the issue for good?

It might not be that simple.

Backing away

The cases on the path to the Supreme Court now differ little from a case justices refused to hear in June, at the same time they made their landmark ruling on the federal law denying tax, health, and other benefits to legally married same-sex couples.

That case, from California, hinged on a constitutional amendment defining marriage as between a man and a woman.

If the justices had acted, it could have struck down gay-marriage prohibitions across the country.

Instead, the justices passed, relying instead on a technical legal argument to resolve the California case and clear the way for same-sex marriage in the state, which resumed at the end of June.

That convinces some that the justices won't take up the issue again so soon. In a way, they have already passed the buck to the states, some say, including language in their Defense of Marriage Act ruling saying it relegates same-sex marriages to second-class status, and "humiliates tens of thousands of children now being raised by same-sex couples."

'Ammunition'

That language makes it clear state bans are ripe for challenge, said Andrew Koppelman, a professor of law and political science at Northwestern University. Language from both Justice Anthony M. Kennedy's majority opinion and Justice Antonin Scalia's biting dissent have appeared prominently in subsequent court challenges and rulings, including in Utah and Ohio.

"The Supreme Court has given them ammunition to go there if that's where they want to go," Koppelman said.

With Utah's ban struck down, 28 states still have constitutional prohibitions on same-sex marriage. Four other states - Pennsylvania, Indiana, West Virginia, and Wyoming - do not permit it through state laws.

More state rulings in favor of gay marriage could be ahead in 2014. The thinking goes, if it can happen in Utah, it can happen anywhere.

A federal judge in Michigan will hear testimony from experts in February before deciding whether to throw out the state's constitutional ban on same-sex marriage. Two federal suits in Virginia, including one being led by the legal team that challenged California's ban, are moving forward.

William Eskridge, a professor at Yale Law School, disagrees with those who say the Supreme Court won't act, predicting justices will get involved in the next year or two.

Different branches of the government are acting, he said - lawmakers, state courts, and federal courts - which could convince the justices to step in.