SPRINGFIELD, Mo. — After a successful vote by the City Council here in October to add sexual orientation and gender identity to the list of categories protected from discrimination here, one supporter, David Trippe, thought this Bible Belt city might have turned a page.

“It took a good deal of courage for six members of the City Council to so clearly state that they thought discrimination in any form was unacceptable and they needed to take a stand,” said Mr. Trippe, who served on a city task force that helped draft the policy.

But in the view of gay rights activists, it did not take long for the page to turn back. On Tuesday, after a nearly five-month campaign by Christian conservatives, voters in this southwest Missouri city narrowly approved a measure to repeal the ordinance.

“We were quite elated to win this,” said Calvin Morrow, the executive director of Christians Uniting for Political Action, a group that led the repeal effort. The push succeeded, 51 percent to 49 percent, in a vote that officials said drew the largest turnout here since 2001.