Current Fannie Mae and Freddie Mac mortgage-backed securities are likely to retain US government backing should Congress create a new system for financing US homes, Federal Reserve Board chairman Ben Bernanke said on Wednesday. The comments follow speculation earlier this month bondholders in the mortgage funding giants seized by the government could ultimately lose some of their investment. “My assumption is the mortgage backed securities which are already outstanding will be grandfathered and will retain the US government backing that they currently have,” Bernanke told lawmakers on the US House Financial Services Committee. “At some point there will be a change in the structure and there will be no more of the current type of MBS created. But the existing MBS I assume will be protected until such time as they either expire or are purchased back,” Bernanke said in response to a question about the future of Fannie and Freddie.