ILLINOIS, MISSOURI, Arkansas, Tennessee and Mississippi are, to the trucking industry, the "barrier states." They bisect the nation and have succeeded, so far, in making transcontinental runs of the biggest of the big trucks -- the 80,000-pound ones -- illegal and, therefore, dangerous. So it was that last February the Senate quietly added a key amendment to a trucking safety bill. It would require all states (nine would be affected) to raise the limit they put on trucks to at least 80,000 pounds or face the loss of federal highway money.

This is a strange twist in the traditional federal-state highway relationship. Before 1966, the states totally regulated the weights and lengths of trucks. In that year, Congress established a maximum weight limit (73,280 pounds) for trucks on the interstate highway system. It did so out of fear that heavier trucks would do too much damage to the highways. In 1974, when the 55-mph speed limit was approved, Congress raised the maximum limit to 80,000 pounds to offset what was perceived to be a shortage of truck capacity because of the longer travel times. Not all states leaped at this opportunity to welcome the bigger trucks, however, and now the truckers are back with this legislation to change the old maximum into a new minimum.

The arguments for and against the proposal are, to say the least, conflicting. State highway officials claim bigger trucks mean much larger highway-repair bills; the truckers minimize the increased damage, arguing that it will be more than offset by the savings in fuel costs. But, the highway people say, trucks traveling on damaged highways burn more fuel than those traveling on good ones.

The best solution for the House is to sidetrack the whole question. A report is due next January from the administration on truck weights and lengths, to be followed by another report a year later on highway costs and who should pay them. At least until that evidence is in, Congress should be leery about telling state legislatures that it knows more about their highway problems than they do.