A majority of the Madison residents in a government program that helps them afford their rents are facing an immediate jump in the portion they pay because of an unexpected change in federal funding.

The increases, which vary widely but exceed 50 percent for some tenants, are triggering worry and panic among recipients and dire predictions among others.

“I simply don’t know what to do,” said Thelma Johnson, 61, a retired housekeeper who lives on Social Security and uses a wheelchair due to a bad knee. Her portion of her $835 monthly rent will go to $288 from $185 on Aug. 1, a 56 percent jump.

The increases affect people receiving Section 8 vouchers, a federal program that helps very-low-income families, the elderly and the disabled afford housing in the private market. Recipients usually pay about 30 percent of their income toward rent, with the government picking up the rest.

The money gets funneled through the city’s housing authority, which recently learned it would receive $9.5 million in Section 8 funding for 2009 instead of the $10.1 million it had counted on. The difference — $578,000 — is what’s causing the pain.

“Some people are angry, and I don’t blame them,” said Agustin Olvera,...