In a letter sent over the weekend, Carter also called Miller's speech "rabid and mean-spirited."
"By now, there are many of us loyal Democrats who feel uncomfortable in seeing that you have chosen the rich over the poor, unilateral pre-emptive war over a strong nation united with others for peace, lies and obfuscation over the truth and the political technique of character assassination as a way to win elections or to garner a few moments of applause."
Carter's office declined to release the letter Tuesday, but Miller's office confirmed the contents.
Miller responded Tuesday by repeating his contention, made in the convention speech last week, that the security of his family outweighed any loyalty to the party where he has spent a lifetime.
"John F. Kennedy warned about the dangers of extreme party loyalty and once said, 'What sins have been committed in its name,"' said Miller, who plans to retire in January as a Democrat. "My first loyalty is and always will be my family."
Carter also defended himself against Miller's accusation in the speech that Carter was a pacifist. Carter said he served in the Navy from 1942 to 1953 and, as president, strengthened the nation's military.
This isn't the first time the two former governors have clashed since Miller began disagreeing with Democrats on key policy matters.
Last December, Carter said Miller had betrayed the principles he thought the two shared. Carter said former Gov. Roy Barnes' (search) decision to appoint Miller to the Senate was a mistake.
In December, Miller called Carter a friend of more than 40 years who had written him at least a dozen personal notes.
"Half of them are giving me hell, and the other half are bragging on me," he said. "So, I figure I'm doing OK batting .500 with Jimmy Carter."