One-parent families, which are among the poorest and most deprived groups in American society increased by 79 percent from 1970 to 1980, the Census Bureau reported yesterday.

Of some 30.4 million families with children, nearly 6 million are headed by one parent, almost invariably a woman.

Poverty rates among one-parent families headed by women are more than triple those among families having both husband and wife, the bureau reported.

Only about 17 million persons live in one-parent families; the vast majority of Americans (75 percent) still live in households headed by a husband and wife.

But the Census Bureau said that the increase in one-parent families is among the most dramatic social developments of the decade.

The figures show that among white families with children, 15 percent (about 4 million) are one-parent families. Though this percentage is relatively small, it is a 75 percent boost since 1970.

Among blacks, the proportion of one-parent families is a staggering 49 percent (1.8 million families). This is 83 percent higher than a decade ago.

Poverty rates among one-parent units are enormously higher than among two-parent groups.

One reason is that women normally earn less than men, according to census expert Arthur Norton. Another is that where there are two parents, both may work. boosting family income. Moreover, single women burdened with child care may be able to work only intermittenly.

Norton said the increase in one-parent families is in part the product of more divorce and separation generally in American society. The rise has tapered off somewhat in the last few years.

Earnings figures show that among all units with children under 18, about 13 percent are under the poverty line ($6,662 for a family of four at the time the surveys were taken). But among female-headed one-parent groups, the figures were 34 percent below the poverty line for whites, 58 percent for blacks.

Contrary to some popular notions, the census figures show that most one-parent families don't involve young women who have never been married. Nearly two-fifths of all these families are headed by divorced women, one-fifth by married but separated women, 12 percent by widows. Only 15 percent are headed by never-married women. The rest are headed by men.