Lowering U.S. mortgage rates through a program relying on Fannie Mae and Freddie Mac is just one of several options the U.S. Treasury is considering to support housing, a senior Treasury official said on Thursday.

"We want to use every tool in the federal government's arsenal," Neel Kashkari, the official in charge of the Treasury's financial rescue efforts, told a congressional field hearing.

Sources told Reuters on Wednesday the Treasury was mulling steps to steady the bruised U.S. housing market by possibly offering mortgages at a fixed 30-year rate of 4.5 percent through Fannie Mae and Freddie Mac.

Kashkari, who said it was important to match the right tool to the right job, said that any program relying on Fannie Mae and Freddie Mac would be separate from programs Treasury was considering to deal with foreclosures.