WASHINGTON — Attorney General Eric H. Holder Jr. called Tuesday for the repeal of laws that prohibit millions of felons from voting, underscoring the Obama administration’s determination to elevate issues of criminal justice and race in the president’s second term and create a lasting civil rights legacy.

In a speech at Georgetown University, Mr. Holder described today’s prohibitions — which in some cases bar those convicted from voting for life — as a vestige of the racist policies of the South after the Civil War, when states used the criminal justice system to keep blacks from fully participating in society.

“Those swept up in this system too often had their rights rescinded, their dignity diminished, and the full measure of their citizenship revoked for the rest of their lives,” Mr. Holder said. “They could not vote.”

Mr. Holder has no authority to enact the changes he called for, given that states establish the rules under which people can vote. And state Republican leaders made clear that Mr. Holder’s remarks, made to a receptive audience at a civil rights conference, would not move them.

“Eric Holder’s speech from Washington, D.C., has no effect on Florida’s Constitution, which prescribes that individuals who commit felonies forfeit their right to vote,” said Frank Collins, a spokesman for Gov. Rick Scott, a Republican.

The speech by Mr. Holder reflects his role as the president’s leading voice on civil rights issues. Mr. Obama has spoken only sporadically about race during his presidency, approaching the subject gingerly.

But Mr. Holder has made racial inequities a consistent theme, and in recent months he has made it clear he sees criminal justice and civil rights as inescapably joined.

He has sued Texas and North Carolina to overturn voter-identification laws that studies show are more likely to keep minorities and the poor from voting. He is pushing Congress to eliminate mandatory minimum sentences for nonviolent drug offenses. And he has encouraged low-level drug criminals sentenced during the crack epidemic to apply for clemency.

“On all the issues that he’s framed, he’s put these two themes together and he sees them very much as intertwined,” said Marc Mauer, executive director of the Sentencing Project, a research group that favors more liberal sentencing policies. “The criminal justice system is the civil rights issue of the 21st century. He hasn’t used those words, but that’s what I hear when I listen to him.”

Mr. Mauer said Mr. Holder was the first attorney general to advocate repealing voting bans. The Justice Department said it knew of no other attorney general who did so.

Like mandatory minimum sentences for crack cocaine offenses, laws banning felons from the voting booth disproportionately affect minorities. African-Americans represent more than a third of the estimated 5.8 million people who are prohibited from voting.

Nearly every state prohibits inmates from voting while in prison. Laws vary widely, however, on whether felons can vote once they have been released from prison. Some states allow voting while on parole, others while on probation.

Some states require waiting periods or have complicated processes for felons to reregister to vote. In Mississippi, passing a $100 bad check carries a lifetime ban from voting.

In four states — Florida, Iowa, Kentucky and Virginia — all felons are barred from the polls for life unless they receive clemency from the governor.

“This isn’t just about fairness for those who are released from prison,” Mr. Holder said. “It’s about who we are as a nation. It’s about confronting, with clear eyes and in frank terms, disparities and divisions that are unworthy of the greatest justice system the world has ever known.”

Mr. Holder’s statements carry little political risk. Congress could pass a law guaranteeing felons the right to vote, but similar proposals have failed before and the Obama administration has not advocated similar legislation, despite Mr. Holder’s comments.

Studies show that felons who have been denied the right to vote were far more likely to have voted for Democrats than for Republicans. In 2002, scholars at the University of Minnesota and Northwestern University concluded that the 2000 presidential election “would almost certainly have been reversed” had felons been allowed to vote.

In Florida, the state that tipped that election, 10 percent of the population is ineligible to vote because of the ban on felons at the polls, Mr. Holder said.

In 2011, Governor Scott required felons to wait five years after completing their sentence before they can apply to vote again.

“For those who are truly remorseful for how they have wrecked families and want to earn back their right to vote, Florida’s Constitution also provides a process to have their rights restored,” said Mr. Collins, the governor’s spokesman.

In Iowa, felons can apply to the governor to restore their voting rights if they can prove they have paid their fines and court costs.

“Iowa has a good and fair policy on restoration of rights for convicted felons,” said Jimmy Centers, a spokesman for Gov. Terry E. Branstad, a Republican. “We don’t have any plans to change the process.”

Kentucky, however, is considering changing its Constitution to allow some felons the right to vote. The proposal passed the Democratic-led House last month, and Republicans, who control the Senate, have indicated a willingness to consider it.

Gov. Steven L. Beshear of Kentucky, a Democrat, says felons — except for violent offenders and sex criminals — should get to vote again once their sentences are complete. He supports the proposal being considered in the Senate, his spokeswoman said Tuesday.

In general, state laws have become more lenient toward felon voting over the past two decades as crime decreased and voters cared less about tough-on-crime policies. More recently, liberal Democrats have found allies among civil libertarians as the Tea Party movement gained momentum.

Senator Rand Paul, a Kentucky Republican and a possible presidential candidate, has endorsed his state’s effort to give felons the right to vote. He has also joined Mr. Holder in calling for reducing the prison population and an end to mandatory minimum sentences for low-level drug crimes.

“His vocal support for restoring voting rights for former inmates shows that this issue need not break down along partisan lines,” Mr. Holder said.

of Mr. Paul.