The percentage of married-with-children households in the United States continued to fall during the decade just ended, the Census Bureau has reported. But the rate of decline was slower than in the 1970s.

The agency, in its report on the characteristics of the American family in 1990, said 26 percent of the nation's 93.3 million households were composed of a married couple and children under age 18.

That number showed a moderate decline in the 1980s from the "traditional" family's 31 percent share at the start of the decade. In the 1970s, the portion of U.S. households composed of mother, father and one or more minor children had fallen more dramatically, from 40 percent.

Steve Rawlings, author of the census report issued Tuesday, described the change as a "stabilization or cooling off."

In many other respects, the report depicted a nation shaking off the breakneck pace of change in the 1970s.

There were 9.7 million single parents in the nation last year, 41 percent more than 10 years earlier. That growth rate is half the 82 percent recorded in the 1970s.

Nearly all the single parents were women. There were 8.4 million one-parent families maintained by the mother in 1990, up 35 percent from 1980. The number of single mothers grew by 82 percent in the 1970s.

The number of divorced mothers grew by 9 percent a year in the 1970s, but by only 1.6 percent annually in the 1980s.

Single-parent households were nearly three times more common among blacks than among whites. But the growth of black single-parent families slowed.

The number of traditional families remained fairly stable throughout the 20-year period: 24.5 million in 1990, 24.2 million in 1980 and 25.5 million in 1970.

But the total number of households grew.

"You could say . . . that all the increase {in households} has taken place outside of traditional families," said Linda Waite, a sociologist with the Rand Corp., a California research group.

Anything that tended to slow the growth in family households also would affect the proportion of traditional families, she said.

For example, late marriage delays the formation of new families and can increase the number of single households. Divorce can increase the number of single households.