Undated (AP) _ BRUSSELS, Belgium (AP) - The European Commission on Wednesday fined six steel companies for forming an illegal price-fixing cartel from May 1986 to October 1988.

French Ugine Aciers de Chatillon et Gueugnon, German Krupp Stahl and Italian Ternie Accial Speciali were each fined 100,000 European currency units, the equivalent of $126,000; German Thyssen Edelstahlwerke and British Steel were each fined 50,000 ecus, or $63,000; and Belgian ALZ was fined 25,000 ecus, or $31,500.

Spanish Acerinox, Swedish Avesta and Finnish Outokumpu were also members of the cartel, the commission said, but the European Commission has no authority over the Scandinavian businesses, and the Spanish company was not fined because Spain was still in the early stage of EC membership at the time and thus limiting its steel exports to other EC countries.

The commission said the nine companies had shared a 17-country market - the 12 EC countries plus a majority of European Free Trade Area countries - where they had agreed on quarterly production quotas.

This cartel ''helped keep prices at a higher level than what would have take place if competition had normally functioned,'' the European executive said.

It added, however, that the fines were low because EC officials had not properly coordinated their job. It admitted that some officials in charge of controling the cartel ignored it.