WASHINGTON (AFP) - US President Joe Biden's pledge to nominate a black woman to the Supreme Court is coming under fire from Republicans even before he unveils his pick, a sign of a potentially testy Senate confirmation battle to come.

Mr Biden, during his 2020 presidential campaign, said the nation's highest court should "look like the country" and it was "long past time" an African-American woman served on the bench.

After Justice Stephen Breyer announced his plan to retire last month, the Democratic President reiterated his vow to replace the liberal stalwart with a black woman.

Mr Biden said he has a "shortlist of nominees who are incredibly well-qualified" and that he would announce his choice before the end of February.

Among the names being circulated are veteran judges from some of the top law schools in the country such as Harvard and Yale.

Conservative Republican lawmakers have pushed back at the notion that the vacancy on the nine-member court should be filled by a black woman.

"Black women are, what, 6 per cent of the US population?" said Senator Ted Cruz, a Republican from Texas who sits on the Senate Judiciary Committee, which will conduct the nomination hearing.

"He's saying to 94 per cent of Americans, 'I don't give a damn about you'," Mr Cruz said. "He's saying, 'If you're a white guy, tough luck. If you're a white woman, tough luck. You don't qualify'."

Senator John Kennedy, a Republican from Louisiana who also sits on the committee, said: "I want a nominee who knows a law book from a J. Crew catalogue.

"I want a nominee who's not going to try to rewrite the Constitution every other Thursday to try to advance a 'woke agenda'."

For Senator Roger Wicker, a Republican from Mississippi, Mr Biden's selection would be the beneficiary of a racially discriminatory "sort of quota".

'Disingenuous'

Since the Supreme Court was established, 107 of the 115 justices have been white men, two have been African-American men and five have been women - four white and one Hispanic.

Mr Douglas Keith, counsel at the Brennan Centre for Justice, said critics were being "disingenuous".

"The idea that Joe Biden is doing anything different than presidents have always done when appointing Supreme Court justices is just incorrect," Mr Keith said.

"Presidents have always made their decision about who to appoint based on some combination of politics and thinking about the very personal characteristics that their nominee would bring to the bench."

Mr Ronald Reagan, a Republican, vowed during his 1980 presidential campaign to name a woman to the court and did so the next year when he nominated Ms Sandra Day O'Connor. She was confirmed 99-0.

Religion has also played a role. During the second half of the 20th century, one seat was tacitly reserved for a Jewish justice and another for a Catholic.

Dr Michael Tesler, a political science professor at the University of California, Irvine, said the negative reaction to Mr Biden's pledge illustrates the growing divide between Republicans and Democrats over the question of racism in the United States.

"This is yet another reminder of the remarkable shift partisans' racial attitudes have undergone in the past decade," Dr Tesler said in an article on FiveThirtyEight.com.

"(Republican Party) politics are increasingly animated by the belief that anti-white discrimination is as big of a problem in American society as biases against racial and ethnic minorities," he said.

Memories of Kavanaugh

With Democrats in control of the Senate, Mr Biden's nominee should win confirmation and it remains to be seen just how contentious the nomination hearing will be.

Republicans have not forgotten the bitter Senate confirmation battle of former president Donald Trump's nominee Brett Kavanaugh, who received only a single Democratic vote after being accused of sexual assault, charges he denied.

And while Mr Cruz, Mr Kennedy and other Republicans have been vocal critics of Mr Biden's selection process, Senator Susan Collins, a Republican from Maine, said the party needs to tread carefully.

"The idea that race and gender should be the No. 1 and No. 2 criteria is not as it should be," Ms Collins told The New York Times.

"On the other hand, there are many qualified black women for this post and given that Democrats, regrettably, have had some success in trying to paint Republicans as anti-black, it may make it more difficult to reject a black jurist."