Just after 10 o'clock this morning, the U.S. Supreme Court will begin hearing arguments in a case that sets in stark contrast two views of how a company should operate. The result may well be a change in legal rules that could kick off a wave of litigation seeking billions of dollars for damages.

The justices are taking a new look at a doctrine laid down in a 1922 ruling involving the rates charged by truck lines to carry flax: Plaintiffs may not base antitrust claims on activities that are overseen by a regulatory agency. In an era in which politicians looked to regulators to protect the public interest, that approach, enunciated in Keogh v. Chicago & Northwestern Railway, seemed like a little more than common sense. Justice Louis D. Brandeis reasoned in the 1922 opinion that because it was up to the Interstate Commerce Commission to be sure that rates were just -- and to order rebates if they were not -- Congress could not have meant for shippers to have, through the antitrust laws, a second route to raise the same issues.

The doctrine, in the 64 years since it was laid down, has been used almost mechanically by the courts to toss out antitrust cases, not just against truckers but virtually any regulated industry. Judges grant motions to dismiss almost any antitrust case involving regulated rates. Just last year, for instance, the U.S. Court of Appeals in Chicago dismissed an antitrust case brought by wheat shippers, even though the Interstate Commerce Commission specifically is denied the authority to judge the reasonableness of the rates that were under attack; the fact that the commission has authority to make sure the rates treat all growers equally was enough to invoke the Keogh bar.

In the case the high court is hearing today, Square D v. Niagra Frontier, shippers claim that five truck lines used threats and coercion to keep competing lines from offering bargain rates on shipments to Ontario, but still the lower courts would not let the suit go forward.

With deregulation the name of the economic game today, however, there's less support for giving regulated industries such extra protection from antitrust suits. The Reagan administration will argue this morning that as common carriers get new freedom to operate -- truckers, for instance, now are able to enter or leave a market without getting ICC approval -- they should be subject to the same sort of scrutiny over how they set prices as are manufacturers. "In this and several other once-prevasively regulated areas, Congress has determined that competition rather than regulation will best serve consumer welfare," the Justice Department told the Supreme Court in a brief filed earlier in the case.

The government and the shippers even have on their side the appellate court judges who ruled that the 1922 precedent forced them to throw out the case against the truckers to Ontario. "While agreeing with appellants that much of the reasoning of Keogh seems outdated, we hold that its language has not been overruled, and that if there is to be an overruling, that task is for the Supreme Court." Even though the Supreme Court justices had refused as recently as November 1984 to reconsider Keogh, that invitation from the U.S. Court of Appeals in New York proved irresistible.

If the high court does remove the Keogh protection, "you have a kind of golden opportunity for anyone to say that virtually any kind of rate case belongs in the antitrust courts," warned Donald L. Flexner, head of the American Bar Association committee on antitrust issues for regulated industries and the lawyer who will argue for the truck lines this morning. A shipper could claim that a meeting among carriers at which rates were set did not conform to all of the regulations of the ICC for such collaborative sessions, and therefore amounted to an illegal conspiracy. "You're able to go back in time many, many years," he noted, so in almost any class action "you're talking about hundreds of millions of dollars." And because the cases are brought under the antitrust laws, any damages awarded automatically are trebled.

As Flexner points out, lawmakers opt for rate regulation because they want other values to have precedence over the lowest possible price. One of those traditionally has been assured service, even over routes that might not be economic for the truck lines. Another consideration is that shippers knew their competitors would pay the same rates that they do; a conglomerate could not use the muscle of its total volume to get a lower price on hauling particular goods.

There's no question that the times have changed and that the assurances of the past no longer are automatically valid. What the justices will decide before midsummer is just how far that change has gone.