Life in the American family is getting better, the U.S. Census Bureau asserted yesterday.

In a report called "The Future of the American Family," the bureau's senior demographer, Paul C. Glick said that many rapid social changes in the recent past -- postponement of marriage, lower birth rates and greater numbers of working wives -- have had beneficial effects on family life.

Delaying marriage increases "the chances that a rational choice of a marriage partner will be made at a more mature age than formerly," he said. And delaying childbirth "is one factor associated with a smaller number of children and fewer unwanted births."

Glick said in an interview that the drop in family size means parents have more time to devote to each child and that the rise in the number of working wives means that, for them, time spent with their children is "a change of pace and more enjoyable."

He predicted in his report, which was first made in testimony before the House Select Committee on Population last May, that during the next two decades there will be a slowdown in social change.

Specifically, the report said that marriage rates are stabilizing, divorce rates are likely to decline and the vast increases in the number of women entering the labor market are apt to taper off.

"During the next decade or two, social pressure may also be expected to diminish for both a working mother and her husband to be employed on a full-time basis," the report added. "Relaxation of pressures in these ways would be expected to increase the quality of marriages that are initiated and of those that remain intact."

The report did not say why pressure for full-time work would lessen, but in the interview Glick said the trend toward flexible work hours "is just beginning, and could lead to a demand for fewer working hours." He noted that men are retiring from their jobs earlier than in the past.

"The increasing demand for an ever-higher standard of living is going to wane," he predicted. "People are starting to realize they don't need two full incomes."

Glick noted that the nation's fertility rate has dropped precipitously from a peak of 3.7 children per family in 1957 to 1.8 now. He said he expects the rate to rise a bit and level off at 2 to 2.3 children per family.

The divorce rate doubled -- from 2.5 to 5 per 1,000 marriages -- between 1965 and 1975, Glick said, adding that "for nearly two years (it)... has been virtually unchanged."

The report said 1.9 million adults live as "unmarried couples of opposite sexes" and account for "a rapidly increasing type of living arrangement" -- an 83 percent increase above the 1970 number of such adults.

Glick offered some figures that throw light on the issue of "your place or mine" -- the couples with an arrangement where a woman lives at the man's place total 1.2 million people; the couples with an arrangement where a man lives at the woman's place total 702,000 people.

However, such couples constituted only 1 percent of U.S. households in 1977, the report said. It noted that 77 percent of Americans were in husband-wife households, 10 percent constituted one-parent households, 7 percent lived alone, 5 percent had "other living arrangements" and 1 percent of the population were in institutions.