More than a third of all Americans -- 78 million people -- must pay so much for housing that they do not have enough money left over for such basic necessities as an adequate supply of food, clothing and medical care, according to a new report on housing in the United States.

The rising cost of housing dramatically outpaced income growth from 1970 to 1987, according to the study by Michael E. Stone, a community planning professor at the University of Massachusetts in Boston. During that period, he said, median rents climbed by 26 percent as median incomes dropped by 13 percent.

Among those who were "shelter poor" in 1987 were 42 percent of all renters, 22 percent of all homeowners and a startling 80 percent of those renter households with incomes between $10,000 and $30,000, Stone said in his report issued this week.

He concluded that formulas used by the government to measure poverty are outdated and understate the housing problems of large families while overestimating the needs of small households.

Stone devised a "shelter poverty" standard to measure the extent of poor Americans' housing problems, using a sliding scale of affordability that varies according to income and household size and type.

The number of people who must pay too much for housing is about the same, Stone concluded, but in many cases they are not the people who housing experts generally have thought they are. His study was published by the Washington-based Economic Policy Institute.

The method used by the government to measure housing affordability problems is based on how much of their income people must spend on housing. Low- and moderate-income families who pay more than 30 percent for rent are eligible for federal assistance to cover the additional cost.

"... Some households can afford less than the traditional 25 percent of income -- indeed, some can afford nothing for housing -- while others can afford more than 25 percent and even more than 30 percent without hardship," Stone said in his report.

The gap between what poor families paid for housing in 1987 and what Stone's formula says they could afford was $92 billion.

Stone's report is certain to add to the debate over federal guidelines for measuring poverty, which have not been updated since the mid-1960s. The Census Bureau adjusts its estimates each year as prices increase but the basic definition of poverty has not been changed. Congress's Joint Economic Committee and the Bush administration's Council of Economic Advisers are investigating the shortcomings of the current formula.

Economist Patricia Ruggles said families have changed over the past 35 years as have services and goods available to them. In a book published this spring by the Urban Institute, she recommended a complete overhaul of the basic guidelines. She said that fewer children lived with a single parent and day care was not a necessity three decades ago, as it is today, because fewer women worked outside their homes. What people consider necessities today, such as telephones and indoor plumbing, were not considered essential then, she said.

Adopting Stone's formula for measuring housing affordability would be a major overhaul. His method shows that many low-income families and households of three or more persons pay less than 25 percent of their incomes for rent "but are nonetheless shelter poor because they still do not have enough left over ... to be able to obtain minimum levels of non-shelter necessities," the report said.

At the same time, people living alone and two-person families with moderate incomes can pay more than 30 percent of their income and have enough left over for "quite adequate levels" of other necessities, Stone found.

Families with four or more members can have incomes of $30,000 or more and still be "shelter poor" under Stone's definition because they must use more of their income for non-housing necessities than smaller households, he said.

The roots of affordability problems lie in unstable housing markets and a volatile mortgage market as well as in causes more often cited, such as cuts in federal funds for subsidized housing and high land costs, Stone said. Problems "created by private, speculative interests in housing and land were already apparent in the 1960s and 1970s," he said.

"Furthermore," he said, "the idealization of individual homeownership in this society should not exempt it from scrutiny."

High costs and interest rates bar many middle-income people from ownership and saddle others with the risk of foreclosure, he said. Homeowner tax benefits also "are highly regressive, flowing almost entirely to homeowners with incomes of over $50,000."