IN BALTIMORE next Thursday the long-awaited White House Conference on Families begins its job of examining how families are doing in America and what the effects of government policy on them are and ought to be. The very scheduling of this conference -- to be held in successive sessions in several cities -- has occasioned a remarkable amount of hassling and bad will among various single-interest groups. They have approached it as a forum in which either to press their views or to defend them against assualt from other quarters. But despite the uproar by the "pro-life" lobby, the abortion rights lobby, the gay rights lobby, the pro-family lobby and all the rest, the conference holds serious promise.

THE MIT-Harvard Joint Center for Urban Studies published a study last week that should be interesting reading for the delegates. The study concludes that there is much more diversity in family structure today than there was 20 years ago -- few families made up of father, mother and young chldren, more single parents, both male and female, and more adults living alone. More women are working outside the home -- especially the mothers of young children. The authors expect these trends to continue and to become even move pronounced in the next 10 years. But -- and this is the point of the conference -- these changes move back toward the historical pattern of American family life, which has been extremely varied.The post-World War II generation was the unusual one: a very large proportion of its members followed the idealized pattern of marrying, having children and settling down.

These trends toward family diversity, then, give no particular cause for alarm. One does wonder, however, whether present governmental policies aren't tipping the incentives against marriage and children more than they should. For example, Social Security benefits for a woman decline if, instead of simply living with a man, she marries him. In addition, income taxes are higher if two employed people are married than if they are simply living together. This "marriage tax" is a well-advertised cost of establishing a traditional family.Admittedly, it is difficult to neutralize the federal incentives that now work against marriage and childbearing and, for that matter, against having women in the work force, but the conference cannot avoid pondering the question.

Some opponents of the White House conference contend that the federal government should not be getting into family-life policies at all. That is absurd. The central question before the conference is how to make the present federal policies -- whether all of us are aware of them or not -- a more benign influence on American family life.