The Post editorial of Dec. 12 "Church, State and Taxes" is mistaken in its description of both the issues in the Abortion Rights Mobilization case before the Supreme Court and the position of Americans United on that case.

ARM has not challenged the right of the Roman Catholic Church to lobby or otherwise speak out on abortion or other issues of public concern. What the group has done is to charge the church with endorsing anti-abortion political candidates in violation of its status as a tax-exempt organization. ARM demands that the Internal Revenue Service act to enforce the provisions of the federal tax code barring partisan political activity by tax-exempt groups. Lobbying and political campaigning are two entirely separate activities.

Americans United has not sided with the Catholic bishops and the IRS on this issue. What we have said is that both ARM and the bishops make important points. We have long opposed the injudicious mixing of religion and politics, and the Catholic Church appears to have ignored this concern.

But we also oppose government intrusion into the internal affairs of churches. We are worried about the court order demanding that the Catholic Church turn over massive amounts of internal documents sought by ARM in its legal initiative.

The thorny legal and procedural issues raised by this case are difficult for the average nonlawyer to understand. The garbled Post editorial did little to help the public gain a better understanding.

ROBERT L. MADDOX

Executive Director

Americans United for Separation of Church and State

Silver Spring