Poverty is the key factor in illegitimate births. Study of Census Bureau data shows that race plays much less of a role

New evidence reinforces the old idea, namely that in the United States births out of wedlock are related primarily to poverty and lack of education, and not to race. The information comes in the form of a study of census statistics. Half of all illegitimate births in America occur in families with incomes below $10,000, the study finds. In 1985 black illegitimacy among these poor families was not quite twice the rate of white poor illegitimacy, according to the study's report of an unpublished US Census Bureau analysis. Other studies indicate that among poor teen-age girls, the rate of illegitimate births for blacks and whites is virtually the same.

The Census Bureau study notes that among Americans of all incomes, the per capita rates of illegitimate births between blacks and whites are also coming closer together, as black rates decline while white rates increase. In the population at large, in 1970 out-of-wedlock births for all black women were seven times higher, per capita, than for white women; by 1984 they were only four times higher.

The study, published Monday in the current edition of Public Opinion, occurs just as racial tensions may be increasing again in the US. In recent months several college campuses have seen ugly racial incidents, which many observers thought were consigned to the history of the 1950s and '60s.

``It's dangerous when we think of distinctions by race,'' says Douglas J. Besharov, one of the authors of the study, ``because then we continue to attribute differences as due to race.'' Mr. Besharov is a resident scholar at the American Enterprise Institute.

During the 1960s and '70s the subject of out-of-wedlock births among minority populations was virtually taboo. Social scientists or politicians who attempted to raise it risked being branded racists.

In the past two years this climate has changed drastically, with much attention focused by the news media, social scientists, and black leaders on the social implications of births by unmarried black women. Besharov and the study's other authors say the new attention being given to the state of the black family is not unwarranted; but concern exists that it may result in, among other things, some white Americans mistakenly attributing the problem to race, not poverty. ``We hope,'' Besharov says, ``that we can help head off a new racism on questions of personal behavior.''

In terms of public policy, another reason exists: to help point the way toward finding a national solution to the problems of illegitimacy and family disintegration. ``When you understand the nature of the problem better,'' Besharov says, ``you're more able to come up with social solutions that will work.''

The new assessment comes as Congress and social experts across the US are trying to figure out what steps should be taken to reform the national welfare system. Both liberals and conservatives generally agree that the current welfare program does little to get poor and unmarried teen-age mothers off the welfare rolls and headed out of poverty.

``The next question that has to be asked,'' Besharov says, ``is: Do current welfare policies encourage, discourage, or are they neutral about the question of having a child out of wedlock?'' It is not only a subject for research, but also a question that few social scientists would even dare to have asked a decade ago.