Alabama was the worst-hit state in last week's storms, with 250 people killed. Elsewhere, 101 people died in Mississippi, Tennessee, Arkansas, Georgia, Virginia and Louisiana.
About 1,700 people were injured in Alabama alone and others were missing after tornadoes crushed homes, flipped cars upside down and tore children from their parents' arms.
To help people get back on their feet, the Department of Agriculture will make homes in rural areas available for rent, said Vilsack.
The U.S. Small Business Administration announced it would make loans of up to $200,000 available to homeowners and up to $2 million for small businesses. It would also make $80 million available in block grants to states.