US President George Bush has chosen a close aide, White House counsel Harriet Miers, for a key Supreme Court vacancy.
Lawyer Harriet Miers has been a longstanding aide to George Bush
If approved by the Senate, Ms Miers - who has never sat as a judge - will take up the place left by Sandra Day O'Connor, who stepped down in July.
Ms Miers, 60, said she was humbled. The Supreme Court is one of the most influential bodies in US public life.
But some of Mr Bush's supporters have expressed concern at her lack of conservative credentials.
Mr Bush's announcement came as the Supreme Court prepared for its first day of work after the summer recess.
The nine-member court will be considering some of the most bitterly contested social issues in the US, including assisted suicide, abortion, same-sex marriage, human cloning and campaign finance law.
Without a judicial record, it is not clear where Ms Miers lies on such contentious issues.
Democrats are likely fight the nomination if they think it tips the court's balance towards the right. Sandra Day O'Connor was considered the holder of a key swing vote on the court.
Speaking from the Oval Office, Mr Bush said the Texan-born lawyer Harriet Miers had "devoted her life to the rule of law and the cause of justice".
MIERS' CAREER PATH
1985: First female president of the Dallas Bar Association
1992: First woman to head the Texas State Bar
1995-2000: Chairwoman of the Texas Lottery Commission
2001: Joins White House staff as president's staff secretary
2003: Appointed Deputy Chief of Staff
2004: Named White House counsel
He also named other justices who had been appointed to the Supreme Court without previous experience on the bench, including the late Chief Justice Rehnquist.
Republican Senate Majority Leader Bill Frist said Mr Bush had picked "another outstanding nominee".
"Ms Miers is honest and hard-working and understands the importance of judicial restraint and the limited role of a judge to interpret the law," he said.
The BBC's Oliver Conway in Washington says Mr Bush appears to have reached out to the middle ground, by picking a woman and by apparently consulting with Democrats before making his decision.
The Senate minority leader, Democrat Harry Reid, who voted against John Roberts as US chief justice in his confirmation vote last week, said he liked Ms Miers.
"In my view, the Supreme Court would benefit from the addition of a justice who has real experience as a practicing lawyer," he said.
But Democrat Charles Schumer, a member of the Judiciary Committee, suggested Ms Miers' lack of a judicial record could cause problems.
"Americans will need to know a lot more about Miers' judicial philosophy and legal background before any vote for confirmation," he said.
Some conservative groups have expressed disappointment with her nomination, saying they had been promised a staunchly conservative candidate.
"The president's nomination of Miers is a betrayal of the conservative, pro-family voters," said the conservative advocacy group Public Advocate.
Ms Miers, 60, has been serving as President Bush's top legal counsel since November 2004.
Monday also sees Chief Justice John Roberts take up the helm of the Supreme Court for the first time.