THE SUPREME COURT, in an unfortunate decision last June, suddenly created a large new obstacle to the enforcement of the antitrust laws. Even if you can prove that you are the victim of a price-fixing conspiracy, the Court said, you cannot recover damages unless you dealt directly with the fixer. In an economy as complex as this country's, with its vast networks of distributors, that is an extremely serious qualification. In many kinds of industry, it effectively eliminates any risk of damage suits over price conspiracies.

This anomaly stands out clearly in the case that the Court heard. The state of Illinois sued the Illinois Brick Co., charging that it had conspired to rig prices of concrete blocks. The state government had let construction contracts, the contractors had hired masonry subcontractors, and it was the subcontractors who actually bought the blocks from Illinois Brick. They presumably passed the price on, through the contractors, to the state.

Since it's not illegal to pass a rigged price on, the state can't sue the middlemen. Legally, the middlemen could sue the manufacturer. But these subcontractors weren't hurt by the conspiracy, if there was one, and in any case they are unlikely to undertake prolonged litigation against their supplier. For all the Court knew, it might have been the grandest conspiracy in the history of concrete blocks. But nobody under the Court's rule, would recover anything.

How in the world did the Court arrive at the decision? Well, six of the justices got tangled up in a misconceived effort to apply the logic of an earlier, different case to this one. They were worried, for one thing, about creating multiple liabilities for price fixers if everyone down the distribution chain could sue for triple damages. But trial judges have broad authority to consolidate cases and require plaintiffs to allocate damages among themselves. That, in fact, was what happened in these cases before the Court suddenly halted them.

Fixing prices is a crime, and people who engage in it risk criminal prosecution by the Justice Department. But the Justice Department cannot monitor every price tag or pursue every complaint of conspiracy. To keep markets free and competitive, there is great public interest in encouraging a second kind of enforcement - the civil suit by the consumer. It's the consumer who has the sharpest interest in fair pricing. Consumers can be individuals or corporations or, as in the Illinois case, governments. The effect of the Court's decision, if it stands, is to make price-fixing much less dangerous to the conspirator.

Corrective legislation has been drafted under the leadership of Sen. Edward Kennedy (D-Mass.), and the Carter administration vigorously supports it. The opposition is coming, as usual, from those business orgainizations that celebrate free competition in theory, but find objections to every attempt at actually enforcing it. The Court's decision is an aberration, with unhappy implications for the American economy. The remedy is a simple two-page bill, and it is needed urgently.