The forum featured nine Democratic presidential candidates. Senator Bernie Sanders of Vermont was the only top-tier candidate who missed the event, having declined the invitation after suffering a heart attack last week, though he addressed the group by video before the forum began.

Their attendance was a clear sign of how gay rights have become an essential part of the party’s platform. Several candidates said they would withhold aid from countries that condone discrimination against the L.G.B.T.Q. community and several said they would consider withholding money from nonprofit groups and schools that do not recognize same-sex couples.

The event featured questions from the audience, many of whom were activists and health and social work professionals, on topics such as family leave for gay couples, violence against transgender people and the conflicts between religious freedom and L.G.B.T.Q. rights.

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Mr. Buttigieg, the first major presidential candidate who is openly gay, released an 18-page plan hours before the forum, saying he would rescind the policy that blocks military veterans from receiving insurance coverage for gender reassignment surgery, and add non-binary gender options on federal documents, including passports.

Onstage, Mr. Buttigieg spoke in personal terms in several of his answers.

“There is no right or wrong way to be gay, to be queer, to be trans,” he said. “I hope that our own community, even as we struggle to define what our identity means, defines it in way that lets everybody know that they belong among us.”

Mr. Buttigieg also talked about his own coming out process.

“What it was like was a civil war, because I knew I was different long before I knew I was gay,” he said, and pointed to the stigmas he still faces, such as the prohibition against blood donations from men who have sex with men. “I can’t lead by example on this one, because my blood is not welcome in this country.”