WASHINGTON -- More than 1,200 pages of Clinton-era White House communications about Supreme Court nominee Sonia Sotomayor were withheld from public release by the former president's adviser, a National Archives spokeswoman said.

The materials are mostly related to former President Bill Clinton's 1998 appointment of Judge Sotomayor, then a federal district judge, to the Second U.S. Circuit Court of Appeals. They apparently include internal assessments of Judge Sotomayor and various political factors related to her nomination, which Senate Republicans stalled for more than a year in a reported effort to diminish her chances for eventual elevation to the Supreme Court.

The Presidential Records Act allows a former president or a designated representative to keep documents from the public that contain discussions about appointments to federal office or show discussions between a president and advisers.

Some of this communication could show the most candid and frank discussion among White House officials about Judge Sotomayor's nomination. But the National Archives, which trumpeted its Thursday release of more than 5,000 pages from Clinton Presidential Library, did not disclose that more than 1,200 pages weren't being released until The Wall Street Journal asked how many documents had been withheld.

Matt McKenna, a spokesman for Mr. Clinton, said by email that Bruce Lindsey, the chief executive officer of the William J. Clinton Foundation, decided which documents to withhold "based upon the Presidential Records Act and based upon the common law privileges of attorney/client and attorney work product."