INDIANAPOLIS — Dominated by Republicans and steeped in traditional values, Indiana seemed among the least likely places to become a battleground in the nation’s debate over same-sex marriage when the legislature overwhelmingly chose in 2011 to push forward a state constitutional amendment barring gay couples from marrying.

But in the two years since, the landscape has shifted as voters, lawmakers and courts began recognizing same-sex marriage in places like Maryland, Minnesota, New Jersey and New Mexico and as the United States Supreme Court declared parts of the federal Defense of Marriage Act unconstitutional. In just the past few days, a federal judge struck down a ban on same-sex marriage in Utah, home of the Mormon Church, and a federal appeals court rejected a request to halt the marriages on Tuesday. A federal judge in Ohio found that same-sex marriages should be recognized on death certificates.

So suddenly Indiana, where lawmakers in the coming weeks are expected to call for the second vote needed to put a ban before voters in the fall elections, is now in a far more tense, unpredictable and closely watched spot than anyone here had imagined — a test case in whether a state will impose new limits on same-sex marriage in this fast-moving political and legal environment.

“What happens in Indiana is critical,” said Brian Brown, president of the National Organization for Marriage, which opposes same-sex marriage. He and other opponents hope the outcome here will reveal that shifts in public sentiment over the last few years are not as widespread as some may think.