Families in the '80s will continue to have fewer children, more members working outside of the home and will devote a higher proportion of there incomes to housing, according to Commerce Department chief economist Courtenay Slater.

"The impact of high inflation," said Slater, "will continue to induce the same kinds of changes in the family that we have seen in the 1970s (low birthrate, increase in new workers and decline in the savings rate), with this difference: Some of the trends do not have much more room to go, so that changes in the 1980s will be smaller and more gradual."

Speaking at last week's American Council of Life Insurance-sponsored conference on "The Impact of Inflation on the Family," Slater cited these three critical variables: the future rate of inflation, the changing nature of the American family and shifts in the population.

"Inflation will be with us during much of the 1980s," she said. "However, I believe there may be less of it as the decade goes on. I'm not that pessimistic . . . to classify inflation among life's unavoidable misfortunes."

The increasing variety of family styles -- including single-parents, couples living together and "child-free" couples -- "makes it impossible to generalize," she said, on what constitutes the typical American family and how inflation will affect it.

"The much venerated 'typical' American family with husband, wife and two minor children presently represents only about 12 percent of all households," said Slater. "By 1990, husband-wife households will have sunk to about 57 percent of all households, compared to 61 percent at present and 71 percent 10 years ago."

Among population shifts she projects for the '80s: An increase in 30- to 50-year-oolds. A slight increase in the number of people over 60, and great increase in those over 85. A continuation of the low birthrate of the '70s.

These demographic shifts "are likely to make families a bit less vulnerable to (inflation)," she predicted. "A considerable share of the population is going to be more mature and experienced, and therefore more productive."

Other trends:

A relative scarcity of entry-level labor because of a decrease in the number of people aged 15 to 25.

Continued pressure on married women to find jobs, with an emphasis on full-time over part-time work. "Although it will be difficult," said Slater, "to match the '70s' phenomenal increase in the number of working women."

A decrease in the "intense speculative demand for housing."

Continuation of "families devoting a high proportion of their income to housing . . . with home-ownership continuing to be a middle-class hedge against inflation."

The two groups who will be hardest hit by inflation in the '80s, said Slater will be "the very aged" and single parents. Women will comprise the majority of people over 80 "and many will be living alone."

Most single-parent families will be headed by women who receive "an extremely modest amount of child support and alimony. In 1975 only one-quarter of divorced, separated and single women received such payments and, among those who did, the average amount received was only about $2,800."

Among other predictions at the daylong conference, this one from Rep. Patricia Schroeder (D-Colo.): "Only one woman in 10 will have the pleasure of deciding to work or not to work. The others will have to work."

American business can help reduce the impact of inflation on families by "extending employee rights in the work place," added Wallace C. Fulton, vice president of The Equitable Life Assurance Society.

"We need to offer families a choice of benefits, counseling services to reduce stress, physical fitness programs, alcohol control programs and money management courses for all employees." *tThe life insurance industry's interest in inflation and the family stems from its realization, said conference chairman Robert Houser, president and chief executive officer of Bankers Life Co., that "family stability is the root on which our business is based.

"Most insurance is sold to protect the family loved ones, spouses, children and relatives. If the family disintegrates, our industry would to a great degree die with it."

Since life insurance consists of "taking in money today and providing it back in the future . . . if future money is so inflated to become meaningless, our product becomes worthless."