Washington ? Homeownership rates for low- and moderate-income working families with children have declined since the late 1970s, even though the overall U.S. homeownership rate has risen, according to a study released Tuesday by an affordable-housing coalition.

The new analysis of already-released government data suggests in part that incomes for these working families haven’t kept pace with soaring housing prices, highlighting a need for government to promote construction of more affordable homes, the Center for Housing Policy says.

Over the last couple of decades, builders have generally erected bigger homes than those built before 1980. “Larger homes tend to be more expensive, and any new supply created tends to be geared toward higher-income people,” said Barbara Lipman, the center’s research director.

The report said 68 percent of all U.S. households were owned in 2001, up from 65.2 percent in 1978. However, the homeownership rate for families with children was 68.4 percent in 2001, down from 70.5 percent 23 years earlier.

The rate for working families with children was 56.6 percent, down from 62.5 percent. “Working families” meant those in which members work the equivalent of a full-time job and earn between the full-time minimum wage of $10,712 a year and up to 120 percent of an area’s median income.

Homeownership rates for working families in 2001 were up somewhat since 1991, but still lower than 1978, suggesting that rising housing costs and a lack of affordable stock may be more important factors, Lipman said.

The median sales price of a new home in 1978 was $55,700, about four times the $14,258 median income of a working family with children, according to census data cited by the group. The median new home in 2001 cost $175,000 — five times the median income of $35,000.

Homeownership rates among families with kids may be affected in part by the increase of more single-parent families today than two decades ago, researchers said. Single-parent homes generally have lower incomes than two-parent homes.

However, homeownership rates also declined for those working families with children in which two or more people worked, the study found.