OKLAHOMA CITY  One of the more unlikely showdowns for the fall elections is taking shape here in this staunchly conservative state, where same-sex marriage is constitutionally banned and the Legislature frequently takes on issues like abortion.

Brittany Novotny, a Democrat and Oklahoma’s first known transgender candidate, is running for a seat in the State House against Sally Kern, the Republican incumbent who gained national attention in 2008 for saying that “the homosexual agenda is just destroying this nation” and that homosexuality was a bigger threat than terrorism.

Both candidates for House District 84 in west Oklahoma City  where Mrs. Kern won by a comfortable margin in 2008 and remains popular  have insisted that Ms. Novotny’s sex will not be an issue in their campaigns. But some of Mrs. Kern’s supporters have voiced concern that the “homosexual lobby” has recruited Ms. Novotny, who identifies as a heterosexual woman.

The group Reclaiming Oklahoma for Christ, which has hosted “Rallies for Sally,” said in a mass e-mail message in June, “The homosexual lobby from across America will be pouring money into this local race in an attempt to make a statement to the country by knocking out an outspoken Christian, pro-family representative.”