THE national census has a big undercount problem, all right - and not just the one contemplated. Ever since the last census in 1980, representatives of minority groups, the poor, and the homeless have insisted that their constituencies are underrepresented in the national head-count. The reasons for the undercount include language barriers, the unorthodox living arrangements of some poor people, and the fear of others that the information will be used against them by other government agencies.
The result is that the allocation of various government funds and benefits can be skewed. States also are concerned about the undercount, since the census figures determine apportionment for congressional districts.
The Census Bureau has taken steps to minimize the undercount, including a special effort this year to count the homeless. While these efforts are not perfect, they should improve the accuracy of the census somewhat. The bureau will also conduct a follow-up survey to adjust for identifiable shortcomings.
But another undercount problem has surfaced, one that the Census Bureau didn't anticipate. The rate of return for the mailed census forms that most Americans received in March - and which were to have been returned by April 1 - is far below projections. Last week the bureau reported that only 55 percent of the forms had been returned. The bureau expected a 70-percent ultimate return rate; now even its lowered projection of a mid-60s return rate looks optimistic.
Part of the difficulty is with bureaucratic gaffes or the mail. But the largest aspect of this other undercount is simply that people are failing to return the forms.
C'mon, America. The form is short; it takes but a few minutes to fill out. There are reasons of self-interest involved, for the accuracy of the census could determine benefits you receive or the weight of your vote. But participation in this once-a-decade national event is also a civic duty. There are lots of good reasons why Americans should know who and where they are in 1990. Do your part.