ALTHOUGH a billion dollars has already been spent and the 1980 census is almost complete, Congress is on the verge of declaring it doesn't want to know the primary numbers of all the counting. The House has passed, and the Senate Appropriations Committee has approved, legislation designed to stop the Census Bureau from calculating the number of seats in the House to which each state will be entitled after 1981.

The purpose of this legislation is to derail the automatic reapportionment of the House that would otherwise occur next January. Under law, the president is required to report to Congress the number of persons living in each state and the number of House seats to which each state is entitled. The president's numbers, under that law, are final and the clerk of the House automatically sends the necessary paper work to the states.

Rather than repeal this law that has worked successfully since 1930, the House attached a rider to the Treasury appropriations bill, barring the executive branch from spending any money to calculate the reapportionment figures or to transmit them to Congress. If this becomes law, presumably the whole reapportionment question will be dumped in the lap of the next Congress.

The situation Congress is trying to create would be comical if its prospective impact were not so serious. Any decent statistician can figure out the new allotment of House seats once the Census Bureau announces its final state-by-state population figures. The president could take a day off from official duties, find a statistician to do the math for him free and write his report to Congress. Transmitting the report to Congress without spending government money might be more difficult, but the president could put it in his pocket and walk it up there.

The ostensible reason for cutting off the automatic reapportionment process is a dispute many members of Congress have with the Census Bureau over who should be counted. The bureau plans to include in its final figures all the people it can find in each state. Some members of Congress want illegal aliens excluded from the totals on which House seats are based.

But the time to have resolved the issue of the illegal aliens is past. If they are to be excluded from the numbers used to redivide House seat, either the census will have to be done over, estimates will have to be used or the whole reapportionment process will have to be deferred until 1991. None of those possibilities is appealing, except maybe to the lawyers who would handle the inevitable litigation and to the members of the House who now hold seats likely to be wiped out if automatic reapportionment occurs.