The value of single-family homes in the United States soared by 95 percent in a six-year period, while the family income of those who owned them rose by only 59 percent, according to a government housing survey released today. At the same time, however, inflation and tax breaks combined to give these owners a virtual "free ride" financially for a time, officials said, but not the brakes are on.

The incidence of home ownership rose by 15 percent, to 51.4 million, during the same period. But the proportion of the household owners in the total population remained almost the same, rising from 64 to 65 percent.

"So, althought there was much concern voiced about the affordability of housing during the 1970s, housing was actually very affordable," said Duane T. McGough, of the Department of Housing and Urban Development, whose office jprepared the report jointly with the Census Bureau, based on a 1979 survey.

"The remarkable thing" is that as the postwar baby boom generation swelled the population with young adults struggling to get a financial foothold, and singles and femaleheaded households grew, "the rate of home ownership didn't decline ," he said. "It was evident that more people were getting into the market than formerly could have."

Monthly costs of owning a home rose 61 percent for homeowners with mortages, and 59 percent for those who owned their homes free and clear, according to the report. These costs included mortgage payments, real estate taxes, property insurance, fuel and utilities.

But the tally ignores the large gains in equity caused by inflation and the substantial tax breaks allowed homeowners, McGough said.

In fact, during much of the 1970s, homeowners were found to have negative costs," McGough said, meaining that they were gaining more financially than they were paying out. As the market slowed nd interest rates shot up, however, those costs have "turned positive," for first-time buyers if not for those already in the market. The pivot point is about 1978. Also, he noted, tax changes under consideration would reduce the value of tax deductions allowed homeowners.

The facts of life for renters seem, by contrast dire. Gross rental costs, including utilities, rose 66 percent, from a median of $133 to $217 a month, while the median family income of renters increased less than 39 percent, to $10,000.

But the figures are a little deciving, McGough said. "Individual renters may have had income rising along with the rents.But there is a changing body of renters."

In other words, the higher-income renter tends to be "skimmed off" into home ownership and is then replaced by a renter with a lower income. As more and more middle-income families managed to buy homes, they left a higher percentage of renters with low incomes.

"The proportion of renters paying more than 25 percent of their income in rent has been creeping up, so they are feeling more of a squeeze," but not as much as the figures imply, McGough said.

The ones who are really feeling the pinch are the landlords, he added. The costs to renters have not gone up as fast as the cost to rental owners, which accounts for the trend toward conversion to condominiums and to abandoning buildings in some cities.

The number of owner-occupied condominiums increased by 91 percent, from about lhalf a million to nearly a million in the six-year period, according to the report.

Among blacks, there were 3.7 million owner households compared with 4.6 million renter households. Home ownership rates for blacks have been consistently lower than those for whites, although officials said the disparity has diminished, primarily since 1940.

Among households of Spanish origin, about 1.7 million were owners and 2.2 million were renters.

The survey, which attempts periodically to inventory the nation's housing, showed among other things that 559,000 American homes have no indoor bathrooms, including 3,000 homes valued at 200,000 or more.

Asked about that figure, which seemed shocking even at today's prices, McGough laughed and said there are some expensive homes with defects that "can be laid to the idiosyncrasy of the owners." More likely, he said, in the nature of surveys, " the figure of 3,000 was probably based on two or three sample cases and blown up to a national number."