In an apparently unprecedented move, President Bush on Wednesday revoked a pardon he had issued 24 hours earlier for a politically connected real estate developer who defrauded hundreds of low- income home buyers -- acknowledging that White House aides had not fully described the scope of the crimes and the context of the clemency application. The issue of presidential pardons has been especially sensitive since President Clinton granted a series of last-minute pardons for well-connected criminals -- most notably fugitive financier Marc Rich, who had been indicted on tax evasion and other charges.