U.S. Treasury Secretary Timothy F. Geithner said taxpayer losses from the Troubled Asset Relief Program are shrinking, and he credited departing TARP chief Herbert Allison with helping the government stabilize financial markets. Allison, the department’s assistant secretary for financial stability, today announced plans to leave the Obama administration and return to Connecticut, saying in a letter to employees today that “it is the right time for me to step down.” Geithner said Tim Massad, the financial stability office’s chief counsel, will be acting TARP administrator.