HOUSTON — Amid the defeat by voters of an ordinance that would have established nondiscrimination protections for gay and transgender people in Houston, Mayor Annise Parker rallied supporters of the measure, telling them the fight was not over.

The Houston Equal Rights Ordinance was soundly rejected Tuesday by a vote of 61 percent to 39 percent. The defeat came after a nearly 18-month battle in the nation’s fourth-largest city that spawned rallies, legal fights and accusations of both religious intolerance and demonization of the lesbian, gay, bisexual and transgender community.

But Parker, who is gay and championed the ordinance, led a crowd of more than 100 people at an election night watch party in downtown Houston in a chant that referenced the ordinance’s nickname, HERO, yelling, “A hero fights for justice.”

“I guarantee that justice in Houston will prevail. This ordinance, you have not seen the last of. We’re united. We will prevail,” Parker said.

Still, the future of the ordinance looked uncertain. Parker is finishing her final two-year term, and it’s unclear if the next mayor and city council will revisit the issue.