The White House is standing by Commerce Secretary Ron Brown -- for now -- in the wake of damaging new allegations by GOP lawmakers concerning Brown's personal finances. President Clinton, asked by reporters today whether Brown's job was at risk, said only:"He's been a great commerce secretary."This week's furor began when a group of GOP senators wrote to Attorney General Janet Reno on Wednesday, asking for an inquiry into whether Brown misled Congress or failed to report information to avoid paying taxes. The flap escalated on Thursday, when Rep. William F. Clinger, (R-Pa.), chairman of the House Committee on Government Reform and Oversight, made public three checks totalling $135,000 which he said Brown had received from a partnership in 1993, but did not disclose as Cabinet officials are required to do. Reno and the FDIC are now investigating the thicket of Republican charges. Are Brown's days in office numbered? "This appears to be the most serious string of charges that he has confronted since taking office," says TIME Washington correspondent Adam Zagorin. "He's becoming a political problem for the Clinton Administration, and I think he had better come up with an explanation."