Forty-two percent of Obama's successful nominations have been women, according to the study. That's well above the rates of President George W. Bush (22 percent) and President Bill Clinton (29 percent), the study found. President Obama is the first president to appoint two women to the Supreme Court.

Obama has successfully appointed a greater percentage of women to federal judgeships than any other president in American history, the study released Tuesday by the left-leaning Alliance for Justice concluded. The study doesn't include the two recent nominees to the U.S. Court of Appeals for the D.C. Circuit—Patricia Millett and Cornelia Pillard. (Neither pick has been confirmed.)

When President Barack Obama nominated two women to a key appeals court last week, he was adding to his lead when it comes to adding women to the federal bench, according to a new study.

"This administration deserves credit for working to create a federal judiciary that more closely reflects the richness and diversity of the American people," said AFJ President Nan Aron.

After Obama's June 4 Rose Garden announcement of three appointments to the D.C. Circuit, AFJ and other groups interested in judicial vacancies met with top administration last week about continuing to fill the federal bench across the country. White House counsel Kathryn Ruemmler and the administration's lawyer in charge of nominations, Chris Kang, attended the meeting.

Currently, three of the eight active judges on the D.C. Circuit—Karen LeCraft Henderson, Judith Rogers and Janice Rogers Brown—are women. Millett, an appellate litigation partner at Akin Gump Strauss Hauer & Feld, and Pillard, who teaches at Georgetown University Law Center, were nominated to the D.C. Circuit simultaneously with U.S. District Judge Robert Wilkins.

There are continuing signs that Republicans will not swiftly allow the confirmation of Obama's D.C. Circuit picks. Senate Minority Leader Mitch McConnell (R-Ky.), in a speech Wednesday on the Senate floor, denied that Obama’s judicial nominees are being treated unfairly.

Senate Majority Leader Harry Reid has raised the possibility of changes to Senate rules on the filibuster to prevent Republicans from blocking the administration's nominees. Republicans filibustered Obama's first nominee to the D.C. Circuit, Caitlin Halligan, for almost three years. She withdrew her name from consideration earlier this year.

McConnell, while not specifically addressing the D.C. Circuit, said the Democrats "intend to manufacture a crisis over nominations as pretext for a power grab."

"Overall, the Senate has confirmed 193 lower court judges and defeated only 2—a .990 batting average," McConnell said today.