A young couple who surmounted the trend

Karen and Curtis Corbin of Boston are an example of a young black family that defies the statistics. After a lengthy, long-distance courtship, ''we decided to get married rather than just live together,'' says Mr. Corbin. ''And we said we'd wait at least two years before having a child.''

Their three-month-old daughter, Amanda, is ''no accident,'' Mrs. Corbin says. ''My baby is wanted - by Curtis and me.'' The couple wants another child later, she says.

''Amanda makes us a real family,'' she says. ''And she wears us both out with her outrageous waking habit - 3 o'clock in the morning,'' adds the new father.

Both Corbins work, Curtis with a development firm and Karen (now on maternity leave) at a television station. It's not unusual in black families for both the husband and wife to work, or for the husband to work two jobs, statistics indicate.

The Corbins, both college graduates, are a case in point. ''When both husband and wife work, a black family is likely to achieve middle-class status; but in more and more black families, there is no husband,'' writes Henry E. Felder of the US Department of Housing and Urban Development in last August's issue of Focus (newsletter of the Joint Center for Political Studies, a black think-tank in Washington). The gap is widening between black families with incomes $25,000 and above and black families with incomes under $10,000, Dr. Felder reported.

''It's difficult to take care of a family today on one salary. So I'm working on my art to supplement my income,'' Curtis says. Karen says she plans to return to work - if ''we find someone to take proper care of Amanda.''