District of Columbia renters overall pay about 8 percent less for their apartments than renters in the nation as a whole, while D.C. homeowners have substantially higher housing costs than people in other parts of the country, a new report by the U.S. Census Bureau shows.

The median rent including utilities in the District was $224 a month, compared with $243 for the nation as a whole, says a report based on data from the 1980 census. Median rents were $310 a month in Maryland and $331 in Virginia.

"That $224 figure really boggles my mind," said D.C. Housing Director James E. Clay. He said he could not immediately account for why the figure would be so low, but said the large amount of subsidized housing in the District and the city's rent control law are probably factors.

"Except for subsidized units, you would have a hard time in almost any section of the city finding one that could be rented for $224," he said.

The differences between the District and the neighboring states would appear to belie the notion that people move out of the city to find cheaper housing, but the averages probably have more to do with the type of housing available in the different jurisdictions, Clay said. Comparable units probably would be more expensive in Washington than in the suburbs, he said.

The report said D.C. homeowners with mortgages paid median housing costs of $399, about 9.5 percent higher than the national median of $366--no surprise in a city long known for its high-priced houses. The costs included mortgage payments, real estate taxes, insurance, utilities and fuel.

Homeowners who have paid off their mortgages had median monthly housing costs of $158, about 23 percent higher than the national median of $128, the report said.

Of 253,143 occupied housing units in the District, close to two-thirds were rental units, the report said.

Byron Christenson, vice president of the Apartment and Office Building Association of Metropolitan Washington, said that the lower-than-average rents the study found in the District are a direct result of the city's rent-control laws.

"My rents would be up by about 10 percent from where they are now" without rent control, he said.

But Christenson also said median rent figures mask a wide discrepancy between what longtime tenants and new tenants pay for the same kind of apartment. Longtime residents may pay 20 percent less than new tenants for identical apartments because of the way rent control works, he said.

The rent-control laws allow landlords to raise rents when a tenant moves out of an apartment, so new tenants may pay about the same rent they would if there were no rent-control laws.

Christenson said he manages one building off Connecticut Avenue where two-bedroom apartments are renting for less than the one-bedrooms because tenants in the larger apartments stay in them while people move frequently from the smaller ones.

The Census Bureau report showed a median 1979 household income of $16,030 in the city as a whole, but there were wide differences in incomes between renters and owners and between blacks and whites.

The figure for renters was $12,383, with 22.1 percent below the poverty line, compared with $26,603 for homeowners. The median household income was $13,625 for blacks, who make up about 70 percent of the District population, and $21,980 for whites.

Median housing costs for white D.C. homeowners were $657, compared with $336 for black homeowners. In Maryland, black homeowners paid more in monthly housing costs than whites, $542 compared with $485, while in Virginia black homeowners paid only slightly less than whites.

The Census Bureau recently released a report showing the nation's elderly have more after-tax income than the general population, but its new housing report shows that in at least some ways the elderly in the District are not living as well as younger city residents.

While more than two-thirds of the housing units in the city have air conditioning, for example, only about one-third of the units occupied by elderly people do.

Overall, about 35 percent of the households in the District do not have a vehicle available, but more than half of the elderly have none available, according to the report.

However, almost half of the elderly in those households owned their homes, a higher proportion than city residents as a whole.

The report also showed that:

Close to half the rental units in the city--77,417--were one-bedroom apartments, while there were 20,945 units with three or more bedrooms, pointing up the difficulty large families have in finding adequate rental housing.

While Washington is generally considered a city with a large transient population, about one-third of all homeowners had lived in their current homes for more than 20 years. About 45 percent had moved in during the 1970s.

Renters were far more mobile, and 26 percent had moved into their homes within the past 15 months, compared with 9 percent of the homeowners.

There were 91,398 households occupying single-family homes, down 7 percent from 1970, and 161,374 households living in multifamily structures, down 1 percent from 1970.

About 7 percent of the District's housing units were built during the 1970s, while 39 percent were built before 1940.

Most people in the District, 57 percent, use gas as their primary source of heat, 10 percent use electricity and 30 percent use fuel oil or kerosene.