WASHINGTON, March 22 (Reuters) – Treasury Secretary Timothy Geithner is expected to lay out the Obama administration’s broad vision for restructuring mortgage finance giants Fannie Mae and Freddie Mac on Tuesday in congressional testimony.

Geithner has said that any specific legislative proposals will not come until 2011 at the earliest. His testimony before the House Financial Services Committee on Tuesday is expected to be the first step in a long journey to make changes to the existing housing finance system.

The government seized Fannie and Freddie at the height of the financial crisis, in what at the time was said to be a temporary measure to ensure credit remained available for homebuyers.

Last fall, the U.S. Government Accountability Office said that move will likely muddy efforts to restructure the two companies, which own or guarantee about half of U.S. residential mortgages.

The GAO said the two government-sponsored enterprises have a mixed record in meeting their mission to foster affordable housing, and that both capital and risk management deficiencies had compromised their safety and soundness.