In 1996, Kathryn Lehman was a soon-to-be married lawyer working for Republicans in the House of Representatives. One of her major accomplishments: helping to write the law that bans federal recognition of same-sex marriages.

Today, Ms. Lehman, 53, no longer has a husband, and no longer identifies as straight. And she is a lobbyist for Freedom to Marry, which is devoted to overturning the very law she helped write, the Defense of Marriage Act.

But Ms. Lehman is still a fervent Republican.

“I’m trying to break the stereotype that all gays and lesbians, especially lesbians, are Democrats,” she said.

Although the Republican Party has long drawn gay men who believe in the party’s message of small government and a strong military, Republican lesbians are a rare political breed.