If The Post hasn't taken leave of its census, it has certainly taken liberty with the facts. In a Feb. 15 editorial, "The Census Undercount," The Post seriously misrepresents the position of the Federation for American Immigration Reform, 41 members of Congress and the states of Kansas and Pennsylvania, which in February brought suit in U.S. District Court in Pittsburgh in order to prevent illegal aliens from being included in the 1990 Census used for congressional apportionment. As counsel to the plaintiffs, it is my responsibility to set the record straight.

It is not FAIR's position to exclude illegal aliens from the total Census count used for block grant dispersal, land-planning use and other myriad uses for which Census data are used. Nor has it ever been FAIR's position that legal immigrants should be excluded from the apportionment base.

FAIR's suit is breathtakingly simple in its premise: that illegal aliens -- foreign nationals living in the United States without the consent of the governed -- should not be allowed to determine the political structure of the United States. As it now stands, the Census Bureau intends to include illegal aliens who may have been in the United States only a few weeks, while excluding servicemen and women risking their lives overseas. We believe such a policy makes little sense and is unconstitutional.

For its part, the Census Bureau does not seem to care that current policy cheapens the vote of U.S. citizens and devalues the status of legal immigrants in the electoral process. Nor is the question an ivory tower abstraction; a 1984 Congressional Research Service study based on U.S. Census Bureau data concluded that because illegal aliens were included in the 1980 Census used for congressional apportionment, Georgia and Indiana each lost a seat to California and New York. The most recent CRS study concludes that if illegal aliens are counted in the 1990 apportionment base, Pennsylvania is likely to lose a seat in Congress while Kansas and West Virginia are threatened.

Is it possible to exclude illegal aliens from the apportionment base? Absolutely.

Every Census question has its own set of instructions. By simply instructing Census respondents not to list undocumented or illegal alien residents of the household, the Census Bureau can develop a legal defendable "core" count of citizen and legal resident aliens for apportionment and another for block grants. The count would be different and fulfill different legal and social needs.

In short, contrary to The Post editorial, excluding illegal aliens from the 1990 Census used for congressional apportionment would not necessarily affect block grant dispersal, nor would it have a chilling effect on the minority count. What it would do is guarantee that the political structure of the United States would be shaped by the legal residents of the United States -- not by the capricious action of the U.S. Census Bureau or the presence of millions of uninvited nationals.

CORDIA STROM Counsel to the Executive Director, Immigration Reform Law Institute Washington