Traditional family life in the United States faces an overwhelming series of changes and disruptions. Divorce rates are skyrocketing. A higher proportion of children are being born to unmarried women. One-parent families are increasing.

Sometimes it seems the challenges to family life in the United States are unique. But they are not. Most of the world's developed countries are experiencing precisely the same developments, as women increasingly move into the labor force, according to a study in the Labor Department's Monthly Labor Review.

"In this century . . . almost all developed countries have seen changes of four principal types: a decline in fertility rates, the aging of the population, erosion of the institution of marriage and a rapid increase in childbirths out of wedlock," Constance Sorrentino wrote.

"Each of these four trends has played a part in the transformation of the modern family," Sorrentino, an economist with the department's Bureau of Labor Statistics, reported.

In some countries these trends are more pronounced than here. Denmark and Sweden, for example, have far higher rates of births among unmarried women. Several have higher rates of unmarried couples living together. Of industrialized nations only Japan seems relatively immune to these trends, Sorrentino wrote, and even there the traditional family is losing ground.

Despite a temporary bump upward during the post-World War II Baby Boom, the number of children being born to each woman during her child-bearing years has declined over the last half century in Japan and the industrial countries of Europe and North America. In 1921 there were an average of 3.3 births per woman in the United States. The rate was similar for women in other industrial countries.

By 1988 it had dropped to 1.9 per woman in the United States, negative population growth. Nine other developed countries had experienced similar drops, Sorrentino found, and the rate of births was even lower in most of them than in the United States -- 1.5 in Holland, 1.3 in Italy, 1.6 in Japan and Denmark and 1.7 in Canada.

"This means that the current population will not even replace itself if current levels of fertility continue," Sorrentino said.

Because life expectancy is increasing at the time birth rates are dropping, the average age of the population is increasing in all countries.

Fewer people are marrying and those who do are getting divorced more often, Sorrentino said, but the trend is far more pronounced in the United States.

"Based on recent divorce rates, the chances of a first American marriage ending in divorce are today about one in two; the corresponding ratio in Europe is about one in three to one in four," according to Sorrentino.

More couples, however, are living together without being married. But this is a phenomenon more prevalent in other countries than in the United States. The percentage of U.S. couples living together who were unmarried grew from 1.2 percent in 1970 to 4.7 percent in 1988. But the rate in Canada and France is 8 percent and in Sweden and Holland, 19 percent.

Except for Japan, the percentage of unmarried women giving birth is growing too. In 1960, unmaried women accounted for 5.3 percent of live births in the United States, a rate similar to other European countries -- except Sweden, where unmarried women accounted for 11.3 percent of births.

By 1986, 23.4 percent of U.S. births were to unmarried women. In Sweden it was 48.4 percent; Denmark 43.9 percent. Unmarried women accounted for about 21 percent of births in France and Britain and 16.9 percent in Canada.

In Japan, unmarried women accounted for 1 percent of births.

As the number of traditional two-parent households with children has dropped, there has been an increase, both absoutely and relatively, in single-parent families with children under 18. In the United States, 22.9 percent of all households with children under 18 were headed by single parents. Elsewhere, that figure ranged from 10.9 percent in France to 20 percent in Denmark. In Japan, only 5.9 percent of households were run by a single parent.

Sorrentino attributed these changes partly to cultural phenomena -- the sexual revolution and women's rights movement -- and partly to the surge in women working outside the home. A variety of factors impelled that surge: better opportunities for women; the need for a second paycheck as the growth of male earnings slowed and increased educational attainment by women.

"Most dramatic has been the rise in labor force participation for women 25 to 34 years of age," the primary child-bearing and child-rearing age, Sorrentino found.