The Justice Department's investigation into bid-rigging by highway and airport contractors seems to be never-ending; it started three years ago in Virginia and Georgia, and grand juries are still at work in 17 states. Last week Justice filed charges against firms and individuals in Georgia and Iowa.

So far, Justice's Antitrust Division has started 176 criminal prosecutions involving 159 corporations and 186 individuals. There have been guilty pleas in more than 130 cases involving 114 corporations and 131 individuals. Sixteen cases involving 28 corporations and 10 individuals are awaiting trial. In the 18 cases that have been tried, 10 corporations and 16 individuals have been convicted and six corporations and nine individuals have been acquitted. Seven corporations and four individuals have pleaded no contest. About $35 million in fines has been collected, and jail sentences totaling more than 36 years have been imposed, Justice said.

The number of contractors involved has reached such proportions that Assistant Attorney General William F. Baxter, in a letter to state attorneys general, suggested that they "consider the competitive consequences" if they forbid a guilty firm or individual from bidding on future projects. Meanwhile, the Federal Highway Administration's construction price index rose 1 percent in the second quarter, only the second quarterly increase in more than two years. Officials have credited the investigation with lowering road-building costs.