The Federal Trade Commission yesterday charged the four producers of lead-based "antiknock" gasoline additives with engaging in illegal, anticompetitive practices.

The complaint filed by the FTC charges the four companies - Ethyl Corp., Du Pont, PPG Industries, Inc., and Nalco Chemical Co. - with keeping their prices uniform by "signaling" future price changes to each other.

Du Pont Chairman Irving S. Shapiro immediately accused the FTC of trying to impose the "personal social views" of commission Chairman Michael Pertchuk and other members of the commission. "The action authorized by the commission does not involve any charge of collusion or conspiracy," Shapiro said. "It is an effort to impose on industry Chairman Pertschuk's personal social views and we await the opportunity to present our position to the federal courts . . ."

The additives in question are sold to gasoline producers who blend it in with their fuel to increase octane levels and prevent potentially harmful engine "knocking" or "pinging."

Industry sales exceeded a half-billion dollars last year, with the products being use of the additives is on the decline, however, because of federal laws mandating a "phase-out" of lead from gasoline for environmental reasons.

In addition to "singaling" the FTC complaint alleges that each company set common prices in other ways. Except for PPG, the companies are alleged to have also used "most favored" customer agreements promising a buyer the lowest price the seller charges other buyers.

The commission also issued a proposed order that would go into effect if the companies are found to have violated the Federal Trade Commission Act as alleged in the complaint.

The order would, among other things, prohibit the practices that are allegedly used by the companies to fix prices.

In a statement released yesterday, FTC Bureau of Competition Director Alfred Dougherty, Jr. called the complaint "an important step in the development of the commission's effort to deal with non-collusive practices that facilitate coordinated pricing in concentrated industries."

Dougherty called the case "a first. Unlike cases brought under the Sherman Act, it does not charge an agreement. Nor does it allege that practices followed by the respondents were artificial in any way."

Instead, Dougherty pointed out, the practices alleged in this case "reduce price competition without providing compensating benefits to competition or other public values."

He added that the case "reflects the bureaus's increasing antitrust enforcement emphasis concerning dominant firms and concentrated industries."