Dozens of prominent Republicans — including top advisers to former President George W. Bush, four former governors and two members of Congress — have signed a legal brief arguing that gay people have a constitutional right to marry, a position that amounts to a direct challenge to Speaker John A. Boehner and reflects the civil war in the party since the November election.

The document will be submitted this week to the Supreme Court in support of a suit seeking to strike down Proposition 8, a California ballot initiative barring same-sex marriage, and all similar bans. The court will hear back-to-back arguments next month in that case and another pivotal gay rights case that challenges the 1996 federal Defense of Marriage Act.