Mr. Bowers, 73, served as attorney general for 16 years, leaving office in 1997. He remains a powerful and respected force among Georgia Republicans, and his voice is expected to carry special resonance in the Republican-dominated legislature.

Whether Mr. Bowers is successful or not, gay rights supporters already see their alliance with him as its own kind of victory — one of the many small, intimate changes of heart that have undergirded their success in winning the right to marry in 36 states and the District of Columbia. (Its status in a 37th state, Alabama, is unclear because of conflicting state and federal court orders.) The holdout states, including Georgia, may be forced to follow suit when the Supreme Court takes up the matter this year.

“I am amazed, and I am actually quite proud of him for having seen the light,” said Kathleen Wilde, an Oregon lawyer who served as co-counsel for Michael Hardwick, the gay man at the heart of the 1986 Supreme Court case.

At a news conference last week, when he called the proposed law “nothing but an excuse to discriminate,” and in an hourlong interview, Mr. Bowers acknowledged that his opinions on gay rights had changed, although he was cagey about the details.

“I know I’ve changed,” said Mr. Bowers, a silver-haired West Point graduate with a rural Georgia drawl and a fondness for salty language, adding that he was not sure why or how. “But I know I’m different. I’m not as mean as I used to be. I know that.”