The economic slowdown occurring across the nation may push many renters into homelessness, according to a new study that found that half of all renter households in most big cities entered the decade with little or no financial cushion.

Many renter households, the study found, teeter on the financial edge each month because their salaries have failed to keep pace with rising housing costs.

For example, workers in four of the largest cities -- Washington, San Francisco, Boston and Los Angeles -- must earn more than $14 an hour, or more than three times the federal minimum wage, to afford to rent a two-bedroom apartment with a safe financial margin for other purchases, the study found.

With such high housing costs, many lower-income renters have little or no savings, the report said, warning that an illness, a check lost in the mail or a layoff can send a family out into the street.

"This report shows that millions of Americans are living on the brink of homelessness," said Cushing Dolbeare, executive director of the Washington-based National Coalition for the Homeless.

"The number of homeless people is bound to go up as the recession deepens," she said.

The study made use of "fair-market" rent statistics compiled by the U.S. Department of Housing and Urban Development nationally to establish the necessary level of housing subsidy for those who receive federal assistance.

For the affordability measurement, the study employed the traditional rule of thumb, also used by federal agencies, that a household should pay only 30 percent of its income for housing so there is enough left over for such other essentials as food, clothing and medical care. Most renters, however, do not earn enough to meet the 30 percent ratio, and most pay a much higher percentage of their income for rent.

The study focused on renters because they are at substantially greater risk of becoming homeless than homeowners, according to the report's authors. While homeowners who are delinquent on their mortgage payments are usually given several months of leeway before their lenders begins foreclosure proceedings, in many states a landlord can begin the eviction process days after the due date on the rent check. Homeowners are also protected because many have equity in their homes that can be liquidated.

Those most at risk of homelessness are renters who are disabled, mentally handicapped, on welfare or working in low-wage jobs, especially if they have no health insurance or sick leave. The report cited a recent survey of homeless families in Chicago that found that 19 percent of them became homeless because their welfare checks had arrived late or were lost in the mail.

Working in certain industries place people in extra jeopardy because wages are so low, according to the report. They include retail and service businesses and low-paying jobs in finance, insurance and real estate, the report said.

For example, average earnings for a retail salesperson were about $195 a week in October 1990, which would permit a monthly housing expenditure of about $252, assuming the traditional ratio of 30 percent of the household's income going for housing. No state in the United States, however, has fair-market rents that low, according to the report.

The states with the biggest gap between income and rents were Massachusetts, Maine, California, Nevada and Vermont, according to the study. In those states, more than 50 percent of all renters are unable to afford a two-bedroom apartment within a comfortable financial margin, the study said.

In the District, Maryland and Virginia, about 46 percent of renters are unable to comfortably afford a two-bedroom apartment.

Fair-market rents for two-bedroom apartments vary widely around the country, according to the survey. They ranged from a low of $390 a month in Arkansas, Kentucky and South Carolina to a high of $710 in Massachusetts.

In the District, the fair-market rent for a two-bedroom apartment was $670, while it was $530 a month in Virginia and $560 a month in Maryland.

Rapidly increasing rents are contributing to renters' woes in some areas, the study found. In Dallas, for instance, fair-market rents have risen 25.7 percent in the past two years, climbing from $421 to $529, while they rose 18.7 percent in Seattle. On average across the nation, fair-market rents rose 8.4 percent in the two-year period.

In a handful of cities, rents declined. They fell 6.2 percent in Pittsburgh, dropping from $436 to $409, and 5.2 percent in Denver, dipping from $502 to $476.

The coalition concluded that immediate action is needed to head off an increase in homelessness. It recommended that inexpensive housing be built to accommodate renters, and that the focus of federal efforts be shifted from addressing the housing and financial needs of the middle-class and wealthy to helping the poor and people with lower-middle incomes.

In particular, it recommended that some tax benefits enjoyed by homeowners, such as the mortgage-interest deduction, property tax deduction and deferral of capital gains on owner-occupied homes, be eliminated or curbed and the money instead be spent building housing for the poor.

"A nation that can spend $500 billion to deal with the savings and loan debacle can certainly spend a fraction of that amount to house the homeless," the report said.