Basic requirements for a fair vote are missing in Florida, he said in Monday's Washington Post.
Reforms passed in the wake of the debacle have not been implemented due to lack of funding and political disputes, Carter added.
"The disturbing fact is that a repetition of the problems of 2000 now seems likely," he said.
"Some basic international requirements for a fair election are missing in Florida," including non-partisan electoral officials and uniformity in voting procedures, he said.
Florida's top election official four years ago also chaired the Bush-Cheney 2000 campaign in the state, and her successor is showing "the same strong bias," Carter charged.
Carter: African Americans are
being disqualified from voting
"A fumbling attempt has been made recently to disqualify 22,000 African Americans [likely Democrats], but only 61 Hispanics [likely Republicans], as alleged felons," he said.
Florida Secretary of State Glenda Hood has also appeared eager to get independent presidential candidate Ralph Nader on this year's state ballot, "knowing that two-thirds of his votes in the previous election came at the expense" of Democrat Al Gore, Carter went on.
"She ordered Nader's name be included on absentee ballots even before the state Supreme Court ruled on the controversial issue," Carter said.
Florida governor Jeb Bush, President George Bush's brother, has "taken no steps to correct these departures from principles of fair and equal treatment or to prevent them in the future," he said.
"It is unconscionable to perpetuate fraudulent or biased electoral practices in any nation," Carter wrote.
"With reforms unlikely at this late stage of the election, perhaps the only recourse will be to focus maximum public scrutiny on the suspicious process in Florida."
The Carter Center has monitored more than 50 international elections, most recently in Venezuela and Indonesia.