Mara Keisling, the executive director of the National Center for Transgender Equality, agreed. “All across America right now there are millions of people who are terrified,” she said.

Mr. Trump has no reputation for personal animosity toward gay people, and the Log Cabin Republicans, a gay and lesbian political organization, congratulated him on his victory. He employed gay people in the Trump Organization, spent most of his life in socially liberal New York City, and surprised some Republicans this year when he said transgender people should “use the bathroom they feel is appropriate,” a view held by few others in the party.

But many L.G.B.T. leaders said they were unmoved by accounts of Mr. Trump’s personal tolerance.

“Even if people believe that about Trump, what is true is he will now be held to the G.O.P. platform,” said Rea Carey, the executive director of the National L.G.B.T.Q. Task Force. She called it the most anti-L.G.B.T. platform in recent memory.

Among its provisions: opposition to same-sex marriage, support for state laws limiting which public bathroom transgender people can use, and support for a parent’s right to subject gay and transgender children to “conversion therapy” to change their sexual orientation or gender identity, a practice the Obama administration has said should be banned for minors.

Ms. Carey called Mr. Trump’s public statements on gay and transgender issues “confusing and conflicting.” As a candidate, Mr. Trump told Fox News that he would “strongly consider” appointing Supreme Court justices who would overturn same-sex marriage but later in the campaign held a rainbow flag onstage and presented himself as gay friendly.