Anticipating a wave of late payments, Jason Hill, chief executive of R.G. Hill & Company, which owns and manages about 1,000 apartments in Northern California, said his company was already preparing to waive late fees and halt evictions for lack of payment. For now, he said, it’s not clear what the extent of the damage will be because the most severe economic fallout happened last week, in the middle of the month, though he assumes it could be bad.

“The vast majority of people in society live paycheck to paycheck, regardless of socioeconomic class, and the economy has come to a complete halt,” he said.

For renters like Ian Browning and his wife, the question isn’t when they will fall behind on their rent but what happens — and where they go — when they do. Mr. Browning, who lives in Brooklyn, manages a restaurant that is closing indefinitely. His wife, a hairdresser, is also gearing up for months with little or no income.

They have two small children, pay $1,900 a month in rent and have a savings account that will cover one month of bills. The couple are in deep trouble — for which Mr. Browning used an unprintable term — “and have no idea what will happen,” he said.

A pronounced slowdown in rent and mortgage payments will have a cascading effect on apartment companies, employees like building superintendents and janitors, and finally state and local government revenues: Money that renters pay landlords goes to mortgage payments and property taxes, along with utilities and other public services.

Members of the Mortgage Bankers Association, a trade group, and other housing-industry figures began telling White House officials this week that the home lending system was on the verge of a crisis that the government needed to head off. They said many homeowners couldn’t miss one or two paychecks before defaulting on their mortgages, according to two people familiar with the talks.

Action to shield those with federally backed mortgages came on two fronts Wednesday: from the Federal Housing Finance Agency — the main regulator for Fannie and Freddie, which effectively guarantee most mortgages given by banks and nonbank lenders — and from HUD, which acts as a guarantor for other mortgages under the Federal Housing Administration’s home loan program.