By secretly settling sexual-harassment complaints against its executive director, the Philadelphia Housing Authority runs the risk of having to repay the federal government for the money it paid out. Under federal guidelines, the U.S. Department of Housing and Urban Development must approve any settlement relating to sexual harassment, regardless of the amount, said spokeswoman Donna White. The payments at the center of the PHA crisis - all made to women who filed complaints against Carl R. Greene - were carried out without the knowledge of the agency's board and without informing HUD, which provides most of its funding.