The Supreme Court’s historic hearing later this month about same-sex marriage is already sparking fresh battles over gay rights as opponents try to limit the impact of what they fear will be an unfavorable decision.

Their realization that same-sex unions could soon become a national reality has set off a scramble to draw a firewall around those who have religious objections, such as Christian florists and bakers who do not want to provide services to gay couples.

The heightened tensions have been felt not only in Indiana, where a high-profile fight pitting religious liberties against gay rights recently played out, but in other states as well.

In Florida, for example, the legislature is debating a bill to permit private adoption agencies with religious objections to decline to place children with same-sex couples. In Springfield, Mo., voters just repealed a city ordinance extending civil rights protections to gay and transgender people, and a similar referendum may be on the ballot this fall in Houston.

Support is also growing for a bill that would bar the federal government from revoking tax benefits of religious institutions and other organizations that oppose same-sex marriage.

Gay rights groups have been hopeful that a Supreme Court victory would give momentum to their broader cause and were already turning to other efforts, including winning federal civil rights protection in housing and employment. But with opponents of gay marriage redoubling their resistance, gay rights groups are recognizing that they have more battles to fight on this front.

“While most of the movement is pretty optimistic about the Supreme Court, I think it’s becoming increasingly clear that that’s not the end of the marriage fight,” said Mara Keisling, executive director of the National Center for Transgender Equality. “We’re seeing some really ugly remnants of the marriage fight cropping up already.”

This new phase of the conflict arises from the expectation, shared by activists on both sides of the issue, that the justices are likely to decide by late June that it is unconstitutional for states to limit marriage to a man and a woman. Court watchers looking for clues to the outcome of the case have noted that the justices have repeatedly declined to stay lower-court decisions allowing gay unions to proceed, a possible indication of support for such marriages.

Social-conservative leaders say their rank and file has been caught off guard as same-sex marriage has swiftly become the norm, not only in places like New York and California but also in Bible Belt bastions such as South Carolina and Oklahoma, which are among the 37 states where same-sex marriage is legal. (It is also legal in the District.)

“We think marriage is in the public good, so we need to work toward that end, but we also need to prepare our people for what happens if the culture and courts go the other direction,” said Russell Moore, president of the Southern Baptist Convention’s Ethics and Religious Liberty Commission.

Groups opposed to gay unions continue to press their arguments against a constitutional right, submitting legal briefs and urging congregations to pray for such an outcome. Some conservative leaders predict that a court ruling legalizing same-sex marriage will mobilize conservative activists as did Roe v. Wade, the 1973 Supreme Court decision legalizing abortion nationally.

“I think there will be civil disobedience in America like you’ve never seen before,” said Calvin Morrow, a leader of the drive to repeal Springfield’s measure barring discrimination against gays and transgender people. “They are kicking a sleeping giant.”

The Springfield City Council had passed the measure in October, adding gay and transgender people to the list of groups that cannot be discriminated against in the workplace, in housing and in public accommodations. But it sparked a groundswell of concern among churchgoers, who viewed it as an attempt to elevate the rights of gays over Christians who object to homosexuality and businesses that may not want to serve same-sex weddings, Morrow said.

Gay rights groups contend that comparisons to Roe v. Wade are exaggerated, citing the enormous jump in recent years in public support for same-sex marriage as evidence that the country is ready. A Wall Street Journal-NBC poll last month found that 59 percent of Americans support same-sex marriage, up from 30 percent in 2004.

Still, the gay rights advocates say, they are prepared for a potentially emotional and protracted battle as the nation adjusts to a new reality in which homosexual and heterosexual unions are viewed legally as identical, simply “marriage.” They acknowledge it could take years for the culture to follow fully, and until then, promoting marriage will continue to be a top priority for the movement.

At the same time, many gay rights groups are shifting their attention to passing anti-discrimination measures at the state and federal levels.

Currently, federal civil rights laws explicitly protect people from being fired, evicted or turned away from businesses on the basis of race, religion and gender but not sexual orientation or gender identity. Nearly half of states and the District, and a host of towns and cities, have sought to at least partially address that disparity, but rights groups say the clash in Indiana highlights the need for a national standard.

They say a favorable marriage decision at the Supreme Court will help, allowing them to raise an irony — that although gay people can marry, they could still lose their jobs simply because of their sexual orientation.

“We want to make sure the lived experience of lesbian, gay and transgender people is meaningful and good and free and hopeful wherever people live,” said Evan Wolfson, president of the group Freedom to Marry and an architect of the strategy to establish a national right to same-sex marriage.

He said the movement will seek to “harness the power of the marriage win to continue moving hearts and minds and making possible the additional legal and political gains we must make to gain full inclusion.”

Another priority will be to address challenges faced by transgender people, who have been left out of some of the gay rights movement’s most high-profile victories. For example, while gay rights activists scored a big win in 2010 with the lifting of the military’s ban on openly gay service members, the policy change did not apply to transgender service members, who still are not permitted to serve.

Even as social conservatives try to prevent further setbacks, some are readying themselves for life in a country where gay marriage is legal.

The Southern Baptist Convention, the nation’s largest protestant Christian denomination, has already organized a conference for July titled “The Gospel and Same-Sex Marriage: Equipping the Church for a Post-Marriage Culture.”

“Of course, as an evangelical Christian I believe in miracles, even last-minute miracles, but I’m not counting on that,” Moore said.

Peyton Craighill contributed to this report.