NEW YORK — The LGBT rights movement’s top legislative priority, a comprehensive nondiscrimination bill, will be introduced in Congress on Wednesday, but the excitement will be tempered by political reality: The bill could well be doomed, at least for this year, by lack of Republican support.

That dynamic mirrors the situation nationwide. Twenty mostly Democratic-run states already have comprehensive nondiscrimination protections for LGBT people, comparable to what the Equality Act would mandate nationally. The protections extend to employment, housing, public accommodations and public services.

The other 30 states — where Republicans hold full or partial power — have balked at taking that step, illustrating that LGBT rights is as polarized along partisan lines as abortion, climate change and other hot button issues.

The result is a patchwork map in the U.S., with a majority of states making it legal for an LGBT person to be fired, evicted or barred from public facilities because of sexual orientation or gender identity.

“No one’s civil rights should be dependent on what ZIP code they live in,” said JoDee Winterhoff of the Human Rights Campaign, a national LGBT rights group.

Opponents of nondiscrimination bills, meanwhile, say that such measures can infringe on religious and other beliefs.

“The Equality Act would undermine the freedom to think and act according to our beliefs,” said Emilie Kao of the conservative Heritage Foundation. Citing recent cases in the news, she said faith-based adoption agencies should be not be required to serve same-sex couples, and entrepreneurs such as bakers and florists should be not be required to provide their services for same-sex weddings.

The Equality Act was first introduced three years ago; it would add gender identity and sexual orientation to existing federal nondiscrimination laws covering such realms as employment, housing, education, and public spaces and services. The new version specifies that the act would cover retail stores, emergency shelters, banks, transportation, pharmacies and legal services.

In Congress, the bill has near-unanimous Democratic backing and seems certain to pass the House, but as of Tuesday afternoon only one Republican, Rep. Brian Fitzpatrick of Pennsylvania, had announced plans to be a co-sponsor. In the GOP-controlled Senate, the bill’s chances appear slim.

“The path forward may require another election,” said James Esseks, director of the American Civil Liberties Union’s LGBT & HIV Project.

Esseks is hopeful that federal courts may broaden some protections for LGBT people, notably with regard to workplace discrimination.