WASHINGTON - (AP) - Elena Kagan was sworn in Saturday as the 112thjustice and fourth woman ever to serve on the Supreme Court.

Chief Justice John Roberts administered the oath to Kagan in abrief private ceremony at the court. Kagan, joined by family andfriends, pledged to faithfully and impartially uphold the law.

Afterward, she smiled broadly as a crowd of onlookers stood andapplauded. "We look forward to serving with you," Roberts said.

Kagan, a former Harvard Law School dean who most recently wassolicitor general, was President Barack Obama's choice to succeedretired Justice John Paul Stevens. Republicans criticized her as apolitical liberal, before the Senate confirmed her this past weekon a vote of 63-37.

She was sworn in twice Saturday by Roberts - reciting one oathas prescribed by the Constitution during a ceremony in a conferenceroom at the court with only her family present. Kagan then reciteda second oath, taken by judges, with her family and friends andreporters present.

Kagan won't be formally installed as a justice until Oct. 1 in acourtroom ceremony at the start of the court's new term. But afterthe oaths taken on Saturday, she will be able to begin assuming herduties as a justice, which include reviewing cases and emergencyappeals filed to the Supreme Court.

Kagan, 50, joins Justices Ruth Bader Ginsburg and SoniaSotomayor on the nine-member court, which often divides 5-4 onhigh-profile cases such as gun rights, discrimination and campaignfinance. The first woman in the court's history, Justice Sandra DayO'Connor, retired in 2005.

Kagan isn't expected to alter the ideological balance of thecourt, where Stevens was considered a leader of the liberals.